The OCPP 1.6J protocol reference.

What a charger and its back office say to each other: all 28 messages with their fields and an example, the 43 configuration keys, what a charger can measure and what goes wrong in practice.

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Messages Configuration keys Measurands Questions

ChargerCharge point Back officeCentral system One WebSocket, JSON

What is OCPP 1.6J?

OCPP, the Open Charge Point Protocol, is a free and open standard of the Open Charge Alliance. It sets how a charger talks to the software that manages it: the Central System in the specification, the back office in the market.

In version 1.6J the charger opens a WebSocket to the back office, and both sides send JSON messages over it. The charger reports its status, its meter values and its sessions. The back office starts and stops sessions, changes settings and sets charging limits.

Because the standard is open, a charger that speaks it can also connect to other back offices that do, depending on model, firmware and configuration. That is what lets you mix brands on one site and move a charger to another back office. To run one charger on several back offices at the same time, use the OCPP proxy.

An open standardFree to implement, maintained by the Open Charge Alliance.
WebSocket and JSONOne connection that stays open, with structured messages.
28 messagesIn six feature profiles, from Core to Remote Trigger.
Both directionsThe charger and the back office each start their own messages.

All 28 OCPP 1.6 messages

Every message is a request from one side and a response from the other, matched by a unique message ID.

Core

Required. Fundamental charge point operations: authorization, transactions, status reporting, configuration, and basic remote control.

Requests authorization for an idTag before allowing charging.

Request

Field	Type	Use	What it holds
idTag	string	Required	The identifier to authorize. At most 20 characters.

Response

Field	Type	Use	What it holds
idTagInfo	object	Required	Authorization information for the idTag.
status	string	Required	Authorization status. One of Accepted, Blocked, Expired, Invalid, ConcurrentTx.
expiryDate	string	Optional	Date/time after which the idTag should be considered expired. A date and time.
parentIdTag	string	Optional	Parent idTag for group authorization. At most 20 characters.

Example

The charger sends

[2, "7f83df9c", "Authorize", {
  "idTag": "04A2B3C4D5E6F7"
}]

The back office answers

[3, "7f83df9c", {
  "idTagInfo": {
    "status": "Accepted"
  }
}]

In OCPP 2.0.1: Authorize

Sent after startup to register with the back office.

Request

Field	Type	Use	What it holds
chargePointVendor	string	Required	Vendor of the charge point. At most 20 characters.
chargePointModel	string	Required	Model of the charge point. At most 20 characters.
chargePointSerialNumber	string	Optional	Serial number of the charge point. At most 25 characters.
chargeBoxSerialNumber	string	Optional	Serial number of the charge box. At most 25 characters.
firmwareVersion	string	Optional	Firmware version of the charge point. At most 50 characters.
iccid	string	Optional	ICCID of the SIM card. At most 20 characters.
imsi	string	Optional	IMSI of the SIM card. At most 20 characters.
meterType	string	Optional	Type of the energy meter. At most 25 characters.
meterSerialNumber	string	Optional	Serial number of the energy meter. At most 25 characters.

Response

Field	Type	Use	What it holds
status	string	Required	Registration status. One of Accepted, Pending, Rejected.
currentTime	string	Required	Current time of the Central System. A date and time.
interval	integer	Required	Heartbeat interval in seconds.

Example

The charger sends

[2, "392b5b40", "BootNotification", {
  "chargePointVendor": "ExampleVendor",
  "chargePointModel": "ExampleModel",
  "firmwareVersion": "1.4.2"
}]

The back office answers

[3, "392b5b40", {
  "status": "Accepted",
  "currentTime": "2026-10-06T09:30:00Z",
  "interval": 300
}]

In OCPP 2.0.1: BootNotification

Changes availability of a connector.

Request

Field	Type	Use	What it holds
connectorId	integer	Required	ID of the connector (0 = entire charge point).
type	string	Required	Requested availability change. One of Inoperative, Operative.

Response

Field	Type	Use	What it holds
status	string	Required	Result of the availability change request. One of Accepted, Rejected, Scheduled.

Example

The back office sends

[2, "be3dcf2e", "ChangeAvailability", {
  "connectorId": 1,
  "type": "Operative"
}]

The charger answers

[3, "be3dcf2e", {
  "status": "Accepted"
}]

In OCPP 2.0.1: ChangeAvailability

Changes a configuration key on the charger.

Request

Field	Type	Use	What it holds
key	string	Required	Configuration key to change. At most 50 characters.
value	string	Required	New value for the configuration key. At most 500 characters.

Response

Field	Type	Use	What it holds
status	string	Required	Result of the configuration change. One of Accepted, Rejected, RebootRequired, NotSupported.

Example

The back office sends

[2, "6fdf2255", "ChangeConfiguration", {
  "key": "MeterValueSampleInterval",
  "value": "60"
}]

The charger answers

[3, "6fdf2255", {
  "status": "Accepted"
}]

In OCPP 2.0.1: SetVariables

Clears the authorization cache on the charger.

Request

No fields: the request is empty.

Response

Field	Type	Use	What it holds
status	string	Required	Result of the cache clear request. One of Accepted, Rejected.

Example

The back office sends

[2, "e993e844", "ClearCache", {}]

The charger answers

[3, "e993e844", {
  "status": "Accepted"
}]

In OCPP 2.0.1: ClearCache

Vendor-specific data exchange.

Request

Field	Type	Use	What it holds
vendorId	string	Required	Identifies the vendor. At most 255 characters.
messageId	string	Optional	Additional identification of the message. At most 50 characters.
data	string	Optional	Vendor-specific data.

Response

Field	Type	Use	What it holds
status	string	Required	Result of the data transfer. One of Accepted, Rejected, UnknownMessageId, UnknownVendorId.
data	string	Optional	Vendor-specific response data.

Example

One side sends

[2, "e1a403d5", "DataTransfer", {
  "vendorId": "com.example"
}]

The other side answers

[3, "e1a403d5", {
  "status": "Accepted"
}]

In OCPP 2.0.1: DataTransfer

Retrieves configuration keys from the charger.

Request

Field	Type	Use	What it holds
key	array	Optional	List of configuration keys to retrieve. items At most 50 characters.

Response

Field	Type	Use	What it holds
configurationKey	array	Optional	List of known configuration keys.
key	string	Required	Configuration key name. At most 50 characters.
readonly	boolean	Required	Whether the key is read-only.
value	string	Optional	Current value of the key. At most 500 characters.
unknownKey	array	Optional	List of requested keys that are unknown. items At most 50 characters.

Example

The back office sends

[2, "02bd00f5", "GetConfiguration", {
  "key": [
    "MeterValueSampleInterval"
  ]
}]

The charger answers

[3, "02bd00f5", {
  "configurationKey": [
    {
      "key": "MeterValueSampleInterval",
      "readonly": false,
      "value": "60"
    }
  ]
}]

In OCPP 2.0.1: GetBaseReport and GetVariables

Periodic keep-alive to let the back office know the charger is online.

Request

No fields: the request is empty.

Response

Field	Type	Use	What it holds
currentTime	string	Required	Current time of the Central System. A date and time.

Example

The charger sends

[2, "83622997", "Heartbeat", {}]

The back office answers

[3, "83622997", {
  "currentTime": "2026-10-06T09:30:00Z"
}]

In OCPP 2.0.1: Heartbeat

Sends periodic or triggered meter readings.

Request

Field	Type	Use	What it holds
connectorId	integer	Required	ID of the connector (0 = main meter).
meterValue	array	Required	One or more meter values with timestamps.
timestamp	string	Required	Timestamp of the meter value. A date and time.
sampledValue	array	Required	One or more sampled values.
value	string	Required	The measured value.
context	string	Optional	Reading context. One of Interruption.Begin, Interruption.End, Sample.Clock, Sample.Periodic, Transaction.Begin, Transaction.End, Trigger, Other.
format	string	Optional	Value format. One of Raw, SignedData.
measurand	string	Optional	Type of measurement. One of Energy.Active.Export.Register, Energy.Active.Import.Register, Energy.Reactive.Export.Register, Energy.Reactive.Import.Register, Energy.Active.Export.Interval, Energy.Active.Import.Interval, Energy.Reactive.Export.Interval, Energy.Reactive.Import.Interval, Power.Active.Export, Power.Active.Import, Power.Offered, Power.Reactive.Export, Power.Reactive.Import, Power.Factor, Current.Import, Current.Export, Current.Offered, Voltage, Frequency, Temperature, SoC, RPM.
phase	string	Optional	Phase to which the measurement applies. One of L1, L2, L3, N, L1-N, L2-N, L3-N, L1-L2, L2-L3, L3-L1.
location	string	Optional	Location of measurement. One of Cable, EV, Inlet, Outlet, Body.
unit	string	Optional	Unit of measurement. One of Wh, kWh, varh, kvarh, W, kW, VA, kVA, var, kvar, A, V, K, Celcius, Celsius, Fahrenheit, Percent.
transactionId	integer	Optional	Transaction to which these meter values apply.

Response

No fields: the response is empty.

Example

The charger sends

[2, "80a15023", "MeterValues", {
  "connectorId": 1,
  "meterValue": [
    {
      "timestamp": "2026-10-06T09:30:00Z",
      "sampledValue": [
        {
          "value": "19840",
          "measurand": "Energy.Active.Import.Register",
          "unit": "Wh"
        }
      ]
    }
  ],
  "transactionId": 4521
}]

The back office answers

[3, "80a15023", {}]

In OCPP 2.0.1: MeterValues

Remotely starts a charging session.

Request

Field	Type	Use	What it holds
idTag	string	Required	The identifier to use for this session. At most 20 characters.
connectorId	integer	Optional	Connector on which to start.
chargingProfile	object	Optional	Charging profile to apply to this session.
chargingProfileId	integer	Required	Unique identifier of this charging profile.
stackLevel	integer	Required	Priority level of the profile (higher = higher priority).
chargingProfilePurpose	string	Required	Purpose of the charging profile. One of ChargePointMaxProfile, TxDefaultProfile, TxProfile.
chargingProfileKind	string	Required	Kind of schedule. One of Absolute, Recurring, Relative.
chargingSchedule	object	Required	The charging schedule.
chargingRateUnit	string	Required	Unit of the charging rate (amps or watts). One of A, W.
chargingSchedulePeriod	array	Required	List of schedule periods.
startPeriod	integer	Required	Start of the period in seconds from the schedule start.
limit	number	Required	Power or current limit during this period. In steps of 0.1.
numberPhases	integer	Optional	Number of phases to use for charging.
duration	integer	Optional	Duration of the schedule in seconds.
startSchedule	string	Optional	Start date/time of the schedule. A date and time.
minChargingRate	number	Optional	Minimum charging rate supported. In steps of 0.1.
transactionId	integer	Optional	Transaction to which this profile applies.
recurrencyKind	string	Optional	Recurrence frequency for recurring profiles. One of Daily, Weekly.
validFrom	string	Optional	Date/time from which the profile is valid. A date and time.
validTo	string	Optional	Date/time after which the profile is no longer valid. A date and time.

Response

Field	Type	Use	What it holds
status	string	Required	Whether the charge point accepted the request. One of Accepted, Rejected.

Example

The back office sends

[2, "b7e2ef8a", "RemoteStartTransaction", {
  "idTag": "04A2B3C4D5E6F7",
  "connectorId": 1
}]

The charger answers

[3, "b7e2ef8a", {
  "status": "Accepted"
}]

In OCPP 2.0.1: RequestStartTransaction

Remotely stops a charging session.

Request

Field	Type	Use	What it holds
transactionId	integer	Required	ID of the transaction to stop.

Response

Field	Type	Use	What it holds
status	string	Required	Whether the charge point accepted the request. One of Accepted, Rejected.

Example

The back office sends

[2, "7fb0afb2", "RemoteStopTransaction", {
  "transactionId": 4521
}]

The charger answers

[3, "7fb0afb2", {
  "status": "Accepted"
}]

In OCPP 2.0.1: RequestStopTransaction

Resets the charge point (hard or soft).

Request

Field	Type	Use	What it holds
type	string	Required	Type of reset to perform. One of Hard, Soft.

Response

Field	Type	Use	What it holds
status	string	Required	Whether the charge point accepted the reset. One of Accepted, Rejected.

Example

The back office sends

[2, "526d688f", "Reset", {
  "type": "Soft"
}]

The charger answers

[3, "526d688f", {
  "status": "Accepted"
}]

In OCPP 2.0.1: Reset

Notifies the back office that a charging session has started.

Request

Field	Type	Use	What it holds
connectorId	integer	Required	Connector on which the transaction started.
idTag	string	Required	Identifier used to start the transaction. At most 20 characters.
meterStart	integer	Required	Meter value at start of transaction (Wh).
timestamp	string	Required	Timestamp when the transaction started. A date and time.
reservationId	integer	Optional	ID of the reservation that was used.

Response

Field	Type	Use	What it holds
idTagInfo	object	Required	Authorization information for the idTag.
status	string	Required	Authorization status. One of Accepted, Blocked, Expired, Invalid, ConcurrentTx.
expiryDate	string	Optional	Date/time after which the idTag should be considered expired. A date and time.
parentIdTag	string	Optional	Parent idTag for group authorization. At most 20 characters.
transactionId	integer	Required	Transaction ID assigned by the Central System.

Example

The charger sends

[2, "2410a6a5", "StartTransaction", {
  "connectorId": 1,
  "idTag": "04A2B3C4D5E6F7",
  "meterStart": 12500,
  "timestamp": "2026-10-06T09:30:00Z"
}]

The back office answers

[3, "2410a6a5", {
  "idTagInfo": {
    "status": "Accepted"
  },
  "transactionId": 4521
}]

In OCPP 2.0.1: TransactionEvent

Reports the current status and any errors of a connector.

Request

Field	Type	Use	What it holds
connectorId	integer	Required	Connector for which the status is reported.
errorCode	string	Required	Error code (NoError if no error). One of ConnectorLockFailure, EVCommunicationError, GroundFailure, HighTemperature, InternalError, LocalListConflict, NoError, OtherError, OverCurrentFailure, PowerMeterFailure, PowerSwitchFailure, ReaderFailure, ResetFailure, UnderVoltage, OverVoltage, WeakSignal.
status	string	Required	Current status of the connector. One of Available, Preparing, Charging, SuspendedEVSE, SuspendedEV, Finishing, Reserved, Unavailable, Faulted.
info	string	Optional	Additional free-text info about the status. At most 50 characters.
timestamp	string	Optional	Timestamp of the status change. A date and time.
vendorId	string	Optional	Vendor-specific identifier. At most 255 characters.
vendorErrorCode	string	Optional	Vendor-specific error code. At most 50 characters.

Response

No fields: the response is empty.

Example

The charger sends

[2, "d9b0420e", "StatusNotification", {
  "connectorId": 1,
  "errorCode": "NoError",
  "status": "Available"
}]

The back office answers

[3, "d9b0420e", {}]

In OCPP 2.0.1: StatusNotification

Notifies the back office that a charging session has stopped.

Request

Field	Type	Use	What it holds
transactionId	integer	Required	ID of the transaction being stopped.
timestamp	string	Required	Timestamp when the transaction stopped. A date and time.
meterStop	integer	Required	Meter value at end of transaction (Wh).
idTag	string	Optional	Identifier that requested the stop. At most 20 characters.
reason	string	Optional	Reason for stopping the transaction. One of EmergencyStop, EVDisconnected, HardReset, Local, Other, PowerLoss, Reboot, Remote, SoftReset, UnlockCommand, DeAuthorized.
transactionData	array	Optional	Array of MeterValue objects (same structure as MeterValues.meterValue).
timestamp	string	Required	Timestamp of the meter value. A date and time.
sampledValue	array	Required	One or more sampled values.
value	string	Required	The measured value.
context	string	Optional	Reading context. One of Interruption.Begin, Interruption.End, Sample.Clock, Sample.Periodic, Transaction.Begin, Transaction.End, Trigger, Other.
format	string	Optional	Value format. One of Raw, SignedData.
measurand	string	Optional	Type of measurement. One of Energy.Active.Export.Register, Energy.Active.Import.Register, Energy.Reactive.Export.Register, Energy.Reactive.Import.Register, Energy.Active.Export.Interval, Energy.Active.Import.Interval, Energy.Reactive.Export.Interval, Energy.Reactive.Import.Interval, Power.Active.Export, Power.Active.Import, Power.Offered, Power.Reactive.Export, Power.Reactive.Import, Power.Factor, Current.Import, Current.Export, Current.Offered, Voltage, Frequency, Temperature, SoC, RPM.
phase	string	Optional	Phase to which the measurement applies. One of L1, L2, L3, N, L1-N, L2-N, L3-N, L1-L2, L2-L3, L3-L1.
location	string	Optional	Location of measurement. One of Cable, EV, Inlet, Outlet, Body.
unit	string	Optional	Unit of measurement. One of Wh, kWh, varh, kvarh, W, kW, VA, kVA, var, kvar, A, V, K, Celcius, Celsius, Fahrenheit, Percent.

Response

Field	Type	Use	What it holds
idTagInfo	object	Optional	Authorization information for the idTag.
status	string	Required	Authorization status. One of Accepted, Blocked, Expired, Invalid, ConcurrentTx.
expiryDate	string	Optional	Date/time after which the idTag should be considered expired. A date and time.
parentIdTag	string	Optional	Parent idTag for group authorization. At most 20 characters.

Example

The charger sends

[2, "b380dc07", "StopTransaction", {
  "transactionId": 4521,
  "timestamp": "2026-10-06T09:30:00Z",
  "meterStop": 19840,
  "idTag": "04A2B3C4D5E6F7"
}]

The back office answers

[3, "b380dc07", {
  "idTagInfo": {
    "status": "Accepted"
  }
}]

In OCPP 2.0.1: TransactionEvent

Remotely unlocks a connector.

Request

Field	Type	Use	What it holds
connectorId	integer	Required	Connector to unlock.

Response

Field	Type	Use	What it holds
status	string	Required	Result of the unlock request. One of Unlocked, UnlockFailed, NotSupported.

Example

The back office sends

[2, "882ccab0", "UnlockConnector", {
  "connectorId": 1
}]

The charger answers

[3, "882ccab0", {
  "status": "Unlocked"
}]

In OCPP 2.0.1: UnlockConnector

Firmware management

Firmware updates and diagnostics upload for remote maintenance of charge points.

Requests the charger to upload diagnostic logs.

Request

Field	Type	Use	What it holds
location	string	Required	URI where diagnostics should be uploaded. An address (URI).
retries	integer	Optional	Number of retries for uploading.
retryInterval	integer	Optional	Seconds between retry attempts.
startTime	string	Optional	Start of the time range for log collection. A date and time.
stopTime	string	Optional	End of the time range for log collection. A date and time.

Response

Field	Type	Use	What it holds
fileName	string	Optional	Name of the diagnostics file. At most 255 characters.

Example

The back office sends

[2, "da7920cd", "GetDiagnostics", {
  "location": "ftp://files.example.com/diagnostics/"
}]

The charger answers

[3, "da7920cd", {}]

In OCPP 2.0.1: GetLog

Reports the status of a diagnostics upload.

Request

Field	Type	Use	What it holds
status	string	Required	Current status of the diagnostics upload. One of Idle, Uploaded, UploadFailed, Uploading.

Response

No fields: the response is empty.

Example

The charger sends

[2, "d1c853b4", "DiagnosticsStatusNotification", {
  "status": "Uploaded"
}]

The back office answers

[3, "d1c853b4", {}]

In OCPP 2.0.1: LogStatusNotification

Reports the status of a firmware update.

Request

Field	Type	Use	What it holds
status	string	Required	Current status of the firmware update. One of Downloaded, DownloadFailed, Downloading, Idle, InstallationFailed, Installing, Installed.

Response

No fields: the response is empty.

Example

The charger sends

[2, "dc9afcb2", "FirmwareStatusNotification", {
  "status": "Installed"
}]

The back office answers

[3, "dc9afcb2", {}]

In OCPP 2.0.1: FirmwareStatusNotification

Instructs the charger to download and install new firmware.

Request

Field	Type	Use	What it holds
location	string	Required	URI where the firmware can be downloaded. An address (URI).
retrieveDate	string	Required	Date/time after which the charger should retrieve the firmware. A date and time.
retries	integer	Optional	Number of retries for downloading.
retryInterval	integer	Optional	Seconds between retry attempts.

Response

No fields: the response is empty.

Example

The back office sends

[2, "a57cc6a2", "UpdateFirmware", {
  "location": "ftp://files.example.com/fw-1.4.3.bin",
  "retrieveDate": "2026-10-07T02:00:00Z"
}]

The charger answers

[3, "a57cc6a2", {}]

In OCPP 2.0.1: UpdateFirmware

Local authorization list

Manage a local authorization list on the charge point for offline authentication.

Retrieves the version number of the local authorization list.

Request

No fields: the request is empty.

Response

Field	Type	Use	What it holds
listVersion	integer	Required	Current version number of the local authorization list.

Example

The back office sends

[2, "ccf23a29", "GetLocalListVersion", {}]

The charger answers

[3, "ccf23a29", {
  "listVersion": 1
}]

In OCPP 2.0.1: GetLocalListVersion

Sends a full or partial update to the local authorization list.

Request

Field	Type	Use	What it holds
listVersion	integer	Required	Version number of this list update.
updateType	string	Required	Whether this is a full replacement or differential update. One of Differential, Full.
localAuthorizationList	array	Optional	List of authorization entries.
idTag	string	Required	The identifier to authorize. At most 20 characters.
idTagInfo	object	Optional	Authorization information for the idTag.
status	string	Required	Authorization status. One of Accepted, Blocked, Expired, Invalid, ConcurrentTx.
expiryDate	string	Optional	Date/time after which the idTag should be considered expired. A date and time.
parentIdTag	string	Optional	Parent idTag for group authorization. At most 20 characters.

Response

Field	Type	Use	What it holds
status	string	Required	Result of the local list update. One of Accepted, Failed, NotSupported, VersionMismatch.

Example

The back office sends

[2, "a23c9563", "SendLocalList", {
  "listVersion": 1,
  "updateType": "Full",
  "localAuthorizationList": [
    {
      "idTag": "04A2B3C4D5E6F7",
      "idTagInfo": {
        "status": "Accepted"
      }
    }
  ]
}]

The charger answers

[3, "a23c9563", {
  "status": "Accepted"
}]

In OCPP 2.0.1: SendLocalList

Reservation

Reserve a connector for a specific user ahead of time.

Cancels an existing reservation.

Request

Field	Type	Use	What it holds
reservationId	integer	Required	ID of the reservation to cancel.

Response

Field	Type	Use	What it holds
status	string	Required	Whether the reservation was cancelled. One of Accepted, Rejected.

Example

The back office sends

[2, "63258356", "CancelReservation", {
  "reservationId": 7
}]

The charger answers

[3, "63258356", {
  "status": "Accepted"
}]

In OCPP 2.0.1: CancelReservation

Creates a reservation on a specific connector.

Request

Field	Type	Use	What it holds
connectorId	integer	Required	Connector to reserve (0 = no specific connector).
expiryDate	string	Required	Date/time when the reservation expires. A date and time.
idTag	string	Required	Identifier for which the reservation is made. At most 20 characters.
reservationId	integer	Required	Unique ID for this reservation.
parentIdTag	string	Optional	Parent idTag for group reservation. At most 20 characters.

Response

Field	Type	Use	What it holds
status	string	Required	Result of the reservation request. One of Accepted, Faulted, Occupied, Rejected, Unavailable.

Example

The back office sends

[2, "62a25d78", "ReserveNow", {
  "connectorId": 1,
  "expiryDate": "2026-10-06T10:00:00Z",
  "idTag": "04A2B3C4D5E6F7",
  "reservationId": 7
}]

The charger answers

[3, "62a25d78", {
  "status": "Accepted"
}]

In OCPP 2.0.1: ReserveNow

Smart charging

Set and manage charging profiles for load balancing, solar integration, and scheduled charging.

Removes one or more charging profiles from the charger.

Request

Field	Type	Use	What it holds
id	integer	Optional	ID of the charging profile to clear.
connectorId	integer	Optional	Connector for which to clear profiles.
chargingProfilePurpose	string	Optional	Purpose of profiles to clear. One of ChargePointMaxProfile, TxDefaultProfile, TxProfile.
stackLevel	integer	Optional	Stack level of profiles to clear.

Response

Field	Type	Use	What it holds
status	string	Required	Whether any profiles were cleared. One of Accepted, Unknown.

Example

The back office sends

[2, "2c436739", "ClearChargingProfile", {}]

The charger answers

[3, "2c436739", {
  "status": "Accepted"
}]

In OCPP 2.0.1: ClearChargingProfile

Requests the combined charging schedule for a connector.

Request

Field	Type	Use	What it holds
connectorId	integer	Required	Connector for which to get the schedule.
duration	integer	Required	Duration in seconds for the requested schedule.
chargingRateUnit	string	Optional	Preferred unit for the schedule. One of A, W.

Response

Field	Type	Use	What it holds
status	string	Required	Whether the charge point can provide the schedule. One of Accepted, Rejected.
connectorId	integer	Optional	Connector to which the schedule applies.
scheduleStart	string	Optional	Start date/time of the composite schedule. A date and time.
chargingSchedule	object	Optional	The composite charging schedule.
chargingRateUnit	string	Required	Unit of the charging rate (amps or watts). One of A, W.
chargingSchedulePeriod	array	Required	List of schedule periods.
startPeriod	integer	Required	Start of the period in seconds from the schedule start.
limit	number	Required	Power or current limit during this period. In steps of 0.1.
numberPhases	integer	Optional	Number of phases to use for charging.
duration	integer	Optional	Duration of the schedule in seconds.
startSchedule	string	Optional	Start date/time of the schedule. A date and time.
minChargingRate	number	Optional	Minimum charging rate supported. In steps of 0.1.

Example

The back office sends

[2, "50bc203f", "GetCompositeSchedule", {
  "connectorId": 1,
  "duration": 3600
}]

The charger answers

[3, "50bc203f", {
  "status": "Accepted"
}]

In OCPP 2.0.1: GetCompositeSchedule

Sends a charging profile to the charger.

Request

Field	Type	Use	What it holds
connectorId	integer	Required	Connector to which the profile applies.
csChargingProfiles	object	Required	The charging profile to install.
chargingProfileId	integer	Required	Unique identifier of this charging profile.
stackLevel	integer	Required	Priority level of the profile (higher = higher priority).
chargingProfilePurpose	string	Required	Purpose of the charging profile. One of ChargePointMaxProfile, TxDefaultProfile, TxProfile.
chargingProfileKind	string	Required	Kind of schedule. One of Absolute, Recurring, Relative.
chargingSchedule	object	Required	The charging schedule.
chargingRateUnit	string	Required	Unit of the charging rate (amps or watts). One of A, W.
chargingSchedulePeriod	array	Required	List of schedule periods.
startPeriod	integer	Required	Start of the period in seconds from the schedule start.
limit	number	Required	Power or current limit during this period. In steps of 0.1.
numberPhases	integer	Optional	Number of phases to use for charging.
duration	integer	Optional	Duration of the schedule in seconds.
startSchedule	string	Optional	Start date/time of the schedule. A date and time.
minChargingRate	number	Optional	Minimum charging rate supported. In steps of 0.1.
transactionId	integer	Optional	Transaction to which this profile applies.
recurrencyKind	string	Optional	Recurrence frequency for recurring profiles. One of Daily, Weekly.
validFrom	string	Optional	Date/time from which the profile is valid. A date and time.
validTo	string	Optional	Date/time after which the profile is no longer valid. A date and time.

Response

Field	Type	Use	What it holds
status	string	Required	Whether the profile was accepted. One of Accepted, Rejected, NotSupported.

Example

The back office sends

[2, "01be9b20", "SetChargingProfile", {
  "connectorId": 1,
  "csChargingProfiles": {
    "chargingProfileId": 10,
    "stackLevel": 0,
    "chargingProfilePurpose": "TxDefaultProfile",
    "chargingProfileKind": "Relative",
    "chargingSchedule": {
      "chargingRateUnit": "A",
      "chargingSchedulePeriod": [
        {
          "startPeriod": 0,
          "limit": 16.0
        }
      ]
    }
  }
}]

The charger answers

[3, "01be9b20", {
  "status": "Accepted"
}]

In OCPP 2.0.1: SetChargingProfile

Remote trigger

Request the charge point to send a specific message on demand.

Requests the charge point to send a specific message immediately.

Request

Field	Type	Use	What it holds
requestedMessage	string	Required	The message the charge point should send. One of BootNotification, DiagnosticsStatusNotification, FirmwareStatusNotification, Heartbeat, MeterValues, StatusNotification.
connectorId	integer	Optional	Connector for which the message should be sent.

Response

Field	Type	Use	What it holds
status	string	Required	Whether the charge point will send the message. One of Accepted, Rejected, NotImplemented.

Example

The back office sends

[2, "4c736efd", "TriggerMessage", {
  "requestedMessage": "StatusNotification"
}]

The charger answers

[3, "4c736efd", {
  "status": "Accepted"
}]

In OCPP 2.0.1: TriggerMessage

OCPP 1.6 configuration keys

ChangeConfiguration sets one key at a time on a charger, and GetConfiguration reads them back. This is where most real-world charger behaviour is decided: how often meter values arrive, what is in them, whether a session survives a network outage, how a cable unlocks.

How the call behaves

Every value is a stringNumbers and booleans too: "60", "true". A JSON number breaks the message schema, and a charger that checks the schema answers with a CallError.
Spell key names as the specification doesThe specification treats key names as case insensitive, but not every charger does, so write MeterValuesSampledData and not metervaluessampleddata.
Some keys need a restartThe charger answers RebootRequired, and it is on you to send a Reset.
Manufacturers add their ownGetConfiguration with an empty key list returns every key a charger supports, including the manufacturer's own. Keys you ask for by name that it does not recognise come back in unknownKey.

The four answers

Accepted: The key is set and active now.
Rejected: The key exists but the value was refused: out of range, wrong format, or read-only on this charger.
RebootRequired: The value is stored but does not apply until the charger restarts.
NotSupported: The charger does not implement this key at all.

All 43 keys, by feature profile

Key	Type	Access	What it does
Core34
AllowOfflineTxForUnknownIdOptional in the spec	boolean	Read and write	Whether the charger starts a transaction for an unknown idTag while it is offline.True keeps a site charging through a network outage, at the cost of sessions you may not be able to bill to anyone.
AuthorizationCacheEnabledOptional in the spec	boolean	Read and write	Whether the charger caches the outcome of earlier Authorize calls.Different from the Local Auth List: the cache fills itself from real authorizations, the list is pushed by the backend.
AuthorizeRemoteTxRequests	boolean	Read	Whether the charger authorizes the idTag in a RemoteStartTransaction before starting.If true, a remote start from the app still needs an Authorize round trip, so a bad idTag fails the start.
BlinkRepeatOptional in the spec	integer	Read and write	How often the charger blinks the lamp during a blink sequence.
ClockAlignedDataInterval	integer	Read and write	Interval for clock-aligned meter values, measured from midnight. 0 disables them.900 gives a reading on every quarter hour. This is the one that feeds MeterValuesAlignedData, and it runs whether or not a car is plugged in.
ConnectionTimeOut	integer	Read and write	How long the charger waits for the driver to plug in after authorizing before it releases the connector.
ConnectorPhaseRotation	CSL	Read and write	Phase rotation per connector, as connectorId.RST notation, for example 0.RST, 1.RST, 2.RTS.Wrong here means wrong phase-level meter values and wrong single-phase load balancing. Worth checking on any three-phase site.
ConnectorPhaseRotationMaxLengthOptional in the spec	integer	Read	Maximum number of items in ConnectorPhaseRotation.
GetConfigurationMaxKeys	integer	Read	Maximum number of keys a single GetConfiguration request may ask for.Ask for more than this and the charger may answer with an error. Send GetConfiguration with no keys at all to get everything it supports.
HeartbeatInterval	integer	Read and write	How often the charger sends a Heartbeat when nothing else is happening.The BootNotification response can override this. On a metered SIM, a short heartbeat is the quiet data cost that adds up.
LightIntensityOptional in the spec	integer	Read and write	Brightness of the charger's lighting, as a percentage.
LocalAuthorizeOffline	boolean	Read and write	Whether the charger authorizes from its local list or cache while offline.
LocalPreAuthorize	boolean	Read and write	Whether the charger starts a transaction from the local list or cache while online, without waiting for the backend.Cuts the wait at the charger, at the cost of the backend not having the final say on every start.
MaxEnergyOnInvalidIdOptional in the spec	integer	Read and write	Energy the charger still delivers after an authorization turns out to be invalid.
MeterValuesAlignedData	CSL	Read and write	Measurands sent in the clock-aligned MeterValues, on the ClockAlignedDataInterval.Same measurand vocabulary as MeterValuesSampledData, different trigger: the clock, not the session.
MeterValuesAlignedDataMaxLengthOptional in the spec	integer	Read	Maximum number of measurands in MeterValuesAlignedData.
MeterValuesSampledData	CSL	Read and write	Measurands sampled during a transaction and sent in MeterValues, on the MeterValueSampleInterval.The single most useful key on this page. See the deep dive below.
MeterValuesSampledDataMaxLengthOptional in the spec	integer	Read	Maximum number of measurands in MeterValuesSampledData.Read this before you build a long list: exceed it and the charger rejects the whole thing.
MeterValueSampleInterval	integer	Read and write	How often, during a transaction, the charger samples MeterValuesSampledData. 0 disables sampling.60 is a sane default. Below 30, with a long measurand list, you are generating a lot of traffic for very little extra insight.
MinimumStatusDurationOptional in the spec	integer	Read and write	Minimum time the charger stays in a status before it reports the next one.Useful against status flapping on chargers that bounce between Preparing and Available.
NumberOfConnectors	integer	Read	Number of physical connectors on this charger.
ResetRetries	integer	Read and write	How often the charger retries a failed reset.
StopTransactionOnEVSideDisconnect	boolean	Read and write	Whether unplugging at the car side stops the running transaction.False means the session stays open after the cable is pulled, which is how you end up with sessions that never end.
StopTransactionOnInvalidId	boolean	Read and write	Whether the charger stops the transaction when the backend rejects the idTag.
StopTxnAlignedData	CSL	Read and write	Clock-aligned measurands added to the transactionData of StopTransaction.
StopTxnAlignedDataMaxLengthOptional in the spec	integer	Read	Maximum number of measurands in StopTxnAlignedData.
StopTxnSampledData	CSL	Read and write	Sampled measurands added to the transactionData of StopTransaction.Keep this short. Everything in it is repeated for every sample of the whole session inside one StopTransaction payload, which is how chargers produce megabyte stop messages that backends reject.
StopTxnSampledDataMaxLengthOptional in the spec	integer	Read	Maximum number of measurands in StopTxnSampledData.
SupportedFeatureProfiles	CSL	Read	Feature profiles this charger implements, for example Core, FirmwareManagement, SmartCharging.The honest answer to what a charger can do. Read it before you promise a customer smart charging.
SupportedFeatureProfilesMaxLengthOptional in the spec	integer	Read	Maximum number of items in SupportedFeatureProfiles.
TransactionMessageAttempts	integer	Read and write	How often the charger retries sending a transaction message the backend did not acknowledge.
TransactionMessageRetryInterval	integer	Read and write	Base wait between those retries. The charger multiplies it by the attempt number.
UnlockConnectorOnEVSideDisconnect	boolean	Read and write	Whether the cable unlocks at the charger when it is unplugged at the car.
WebSocketPingIntervalOptional in the spec	integer	Read and write	Interval for WebSocket ping frames on the OCPP-J connection.The quiet fix for chargers that keep dropping offline behind a NAT or firewall that closes idle connections.
Local authorization list3
LocalAuthListEnabled	boolean	Read and write	Whether the local authorization list is in use.
LocalAuthListMaxLength	integer	Read	How many entries the local authorization list holds.
SendLocalListMaxLength	integer	Read	How many entries fit in a single SendLocalList message.A list bigger than this has to be sent in several differential updates.
Reservation1
ReserveConnectorZeroSupportedOptional in the spec	boolean	Read	Whether the charger accepts a reservation on connector 0, meaning any connector.
Smart charging5
ChargeProfileMaxStackLevel	integer	Read	Highest stack level the charger accepts on a charging profile. Higher levels win.
ChargingScheduleAllowedChargingRateUnit	CSL	Read	Which units the charger accepts in a charging schedule: Current (A), Power (W), or both.Send a profile in watts to a charger that only takes amps and it is rejected. This key tells you which to use.
ChargingScheduleMaxPeriods	integer	Read	Maximum number of periods in one charging schedule.
ConnectorSwitch3to1PhaseSupportedOptional in the spec	boolean	Read	Whether the charger can switch between three-phase and single-phase charging.Decides whether you can throttle below the three-phase minimum instead of pausing altogether.
MaxChargingProfilesInstalled	integer	Read	How many charging profiles can be installed at once.

MeterValuesSampledData: what a charger measures

One key, MeterValuesSampledData, decides what telemetry you get out of a charging session. It is a comma-separated list of measurands, and the charger samples every item on it at the interval set by MeterValueSampleInterval, then sends them in a MeterValues message. Leave it at the default and you get one cumulative energy reading, enough to bill, and nothing else: no power curve, no per-phase current, no voltage, no way to see whether a smart charging limit landed.

It never works alone. MeterValueSampleInterval sets how often it fires, MeterValuesSampledDataMaxLength caps how many measurands you may list, StopTxnSampledData decides which of them get repeated inside StopTransaction, and MeterValuesAlignedData is the same vocabulary on a clock schedule instead of a session.

The measurands

Any of these may appear in the list. Which ones a charger supports depends on its hardware: an AC wallbox usually does not report state of charge, and a basic charger may only have the energy register.

Measurand	Unit	Typically on	What it gives you
Energy.Active.Import.Register	Wh	AC and DC	Cumulative energy drawn from the grid, read straight off the meter register. The default when MeterValuesSampledData is empty, and the value nearly every billing calculation is built on.
Energy.Active.Export.Register	Wh	V2G capable	Cumulative energy fed back, for bidirectional setups.
Energy.Active.Import.Interval	Wh	AC and DC	Energy imported since the previous sample, rather than a running total.
Energy.Reactive.Import.Register	varh	Meter dependent	Cumulative reactive energy imported.
Power.Active.Import	W	AC and DC	Instantaneous active power. What you plot to see a charging curve, and what load management reacts to.
Power.Offered	W	AC and DC	Power the charger is currently offering the car. Compare it with Power.Active.Import to see whether a limit is actually being applied.
Power.Reactive.Import	var	Meter dependent	Instantaneous reactive power.
Power.Factor	ratio	Meter dependent	Ratio of active to apparent power.
Current.Import	A	AC and DC	Current drawn. Usually reported per phase, so this one measurand can become three values per sample.
Current.Offered	A	AC and DC	Current limit the charger is signalling to the car. The direct read-out of whether your smart charging profile landed.
Current.Export	A	V2G capable	Current fed back, for bidirectional setups.
Voltage	V	AC and DC	Supply voltage, per phase on three-phase chargers. Useful for spotting a dropped phase or a weak connection.
Frequency	Hz	Meter dependent	Grid frequency. Note that the spec gives it no unit field.
Temperature	Celsius	Charger dependent	Temperature at the charger or connector. Explains derating on a hot day before anyone calls it a fault.
SoC	%	DC, or ISO 15118 on AC	State of charge of the car's battery. Only present when the car actually reports it, which on plain AC charging it usually does not.
RPM	rpm	Rare	Fan speed, on chargers that report it.

Lists that work

Copy one into the value of a ChangeConfiguration call. Start narrow, and add measurands once the charger accepts them.

Billing only
The minimum that still produces a correct invoice. The default on most chargers.
Energy.Active.Import.Register
Standard telemetry
Sensible default for a managed AC site: a power curve, per-phase current and voltage for diagnosis.
Energy.Active.Import.Register, Power.Active.Import, Current.Import, Voltage
Smart charging
Adds the offered values, so you can see whether a profile is actually being applied rather than assuming.
Energy.Active.Import.Register, Power.Active.Import, Power.Offered, Current.Import, Current.Offered, Voltage
DC fast charging
Adds state of charge and temperature, which DC chargers do report and which explain most derating.
Energy.Active.Import.Register, Power.Active.Import, Current.Import, Voltage, SoC, Temperature

What goes wrong

One bad measurand rejects the whole list
Chargers validate the list as a unit. If a single item is unsupported you get Rejected or NotSupported for everything, with no indication which one failed. Set the list one measurand at a time to find the offender, or read MeterValuesSampledDataMaxLength and the vendor documentation first.
One measurand can be three values
Current.Import and Voltage are reported per phase, so on a three-phase charger they arrive as three sampledValue entries each, tagged L1, L2, L3 or L1-N and so on. A list of six measurands can easily be a dozen values per sample. Payload size grows faster than the list length suggests.
Wh against kWh
The energy register is Wh by default, but the unit field can say kWh and some firmware does that. Read the unit rather than assuming it, or you get an invoice that is off by a factor of a thousand.
A short interval is not free
MeterValueSampleInterval at 10 seconds with a long list means hundreds of messages per session. On a metered SIM that is real money, and on a large site it is real backend load. 60 seconds is a good default, 300 for sites where you only need the shape of the curve.
StopTxnSampledData is the payload trap
Everything listed there is repeated, for every sample of the entire session, inside a single StopTransaction message. A long list on a long session produces a payload big enough for backends to reject or truncate, and the transaction then fails to close cleanly. Keep it to the energy register unless you have a specific reason.
Drop the energy register and billing breaks
If Energy.Active.Import.Register is not in the list, the periodic meter values carry no cumulative total. Most backends then fall back to meterStart and meterStop from the transaction messages, and any session where StopTransaction goes missing becomes unbillable. Keep it in the list, always.
SoC is usually not available on AC
State of charge comes from the car, over ISO 15118 or the DC charging protocol. On a plain AC wallbox without Plug and Charge the car does not report it, so requesting SoC either gets rejected or returns nothing useful.
Read the context field
Each sampledValue carries a context: Sample.Periodic, Transaction.Begin, Transaction.End, Sample.Clock or Trigger. A value at Transaction.Begin is a starting register, not consumption. Treating every sample as periodic is how sessions end up double-counted.

Questions about OCPP 1.6J

OCPP 1.6J is version 1.6 of the Open Charge Point Protocol in its JSON form. The charger opens a WebSocket to its back office, and both sides send JSON messages over it. The Open Charge Alliance published version 1.6 in 2015, and most chargers still support it: in our charger database, 483 of the 495 chargers with a known OCPP version support 1.6.

They carry the same messages in a different way. 1.6J sends JSON over a WebSocket that the charger keeps open, so the charger only needs an outgoing connection. 1.6S sends SOAP over HTTP, and then the back office also has to be able to reach the charger.

2.0.1 is a newer version with its own set of messages. It describes a charger's settings in a device model, has security profiles built in, replaces StartTransaction and StopTransaction with TransactionEvent and adds messages for Plug and Charge (ISO 15118). The two do not mix: a charger and its back office agree on one version when the connection opens. In our charger database, 102 chargers list 2.0.1 as well as or instead of 1.6. Every 2.0.1 and 2.1 message is in the OCPP 2.0.1 and 2.1 reference.

The Open Charge Alliance publishes it free of charge on its website, with a JSON schema for every message. This reference follows that specification. Where the two differ, the specification is right.

Through the Smart Charging profile. The back office sends SetChargingProfile with a schedule of limits in amps or watts. A ChargePointMaxProfile caps the whole charger, a TxDefaultProfile applies to every new session and a TxProfile to one running session. When two profiles with the same purpose overlap, the one with the higher stackLevel wins. How Plugchoice uses this is on the smart charging page.

Look it up in the charger database: 775 chargers, with the OCPP versions we know of and where each came from. The charger's datasheet usually says it too, often as OCPP 1.6J or OCPP 1.6 JSON.

In the charger's settings, often in the installer app or on its local web page, enter the back office's WebSocket URL (it starts with ws:// or wss://) and the charger's ID, the charge point identity. The charger opens the connection and sends a BootNotification. Once the back office answers Accepted, the charger is online and sends a StatusNotification for each connector.

Plugchoice and OCPP

A free back officeConnect an OCPP 1.6J charger and manage it in the web portal.
The appOwners and installers control the same charger from their phone.
The OCPP proxyOne charger on several back offices at the same time.
Back officesThe back offices you pick from a list when you connect a charger.

Run your OCPP chargers on Plugchoice

Connect your OCPP 1.6J chargers to Plugchoice for free and manage them in the web portal and the app, and through the API.

Start for free See the OCPP proxy

The OCPP 1.6J protocol reference.

What is OCPP 1.6J?

All 28 OCPP 1.6 messages

Core

AuthorizeRequests authorization for an idTag before allowing chargingCharger to back office

Request

Response

Example

BootNotificationSent after startup to register with the back officeCharger to back office

Request

Response

Example

ChangeAvailabilityChanges availability of a connectorBack office to charger

Request

Response

Example

ChangeConfigurationChanges a configuration key on the chargerBack office to charger

Request

Response

Example

ClearCacheClears the authorization cache on the chargerBack office to charger

Request

Response

Example

DataTransferVendor-specific data exchangeBoth ways

Request

Response

Example

GetConfigurationRetrieves configuration keys from the chargerBack office to charger

Request

Response

Example

HeartbeatPeriodic keep-alive to let the back office know the charger is onlineCharger to back office

Request

Response

Example

MeterValuesSends periodic or triggered meter readingsCharger to back office

Request

Response

Example

RemoteStartTransactionRemotely starts a charging sessionBack office to charger

Request

Response

Example

RemoteStopTransactionRemotely stops a charging sessionBack office to charger

Request

Response

Example

ResetResets the charge point (hard or soft)Back office to charger

Request

Response

Example

StartTransactionNotifies the back office that a charging session has startedCharger to back office

Request

Response

Example

StatusNotificationReports the current status and any errors of a connectorCharger to back office

Request

Response

Example

StopTransactionNotifies the back office that a charging session has stoppedCharger to back office

Request

Response

Example

UnlockConnectorRemotely unlocks a connectorBack office to charger

Request

Response

Example

Firmware management

GetDiagnosticsRequests the charger to upload diagnostic logsBack office to charger

Request

Response

Example

DiagnosticsStatusNotificationReports the status of a diagnostics uploadCharger to back office

Request

Response

Example

FirmwareStatusNotificationReports the status of a firmware updateCharger to back office

Request

Response