This document describes the current stable version of Celery (3.1). For development docs, go here.

Task Messages

Message format

  • task

    Name of the task. required

  • id

    Unique id of the task (UUID). required

  • args

    List of arguments. Will be an empty list if not provided.

  • kwargs

    Dictionary of keyword arguments. Will be an empty dictionary if not provided.

  • retries

    Current number of times this task has been retried. Defaults to 0 if not specified.

  • eta
    string (ISO 8601):

    Estimated time of arrival. This is the date and time in ISO 8601 format. If not provided the message is not scheduled, but will be executed asap.

  • expires
    string (ISO 8601):

    New in version 2.0.2.

    Expiration date. This is the date and time in ISO 8601 format. If not provided the message will never expire. The message will be expired when the message is received and the expiration date has been exceeded.


Extensions are additional keys in the message body that the worker may or may not support. If the worker finds an extension key it doesn’t support it should optimally reject the message so another worker gets a chance to process it.

  • taskset

    The taskset this task is part of (if any).

  • chord

    New in version 2.3.

    Signifies that this task is one of the header parts of a chord. The value of this key is the body of the cord that should be executed when all of the tasks in the header has returned.

  • utc

    New in version 2.5.

    If true time uses the UTC timezone, if not the current local timezone should be used.

  • callbacks

    New in version 3.0.

    A list of subtasks to apply if the task exited successfully.

  • errbacks

    New in version 3.0.

    A list of subtasks to apply if an error occurs while executing the task.

  • timelimit
    <tuple>(float, float):

    New in version 3.1.

    Task execution time limit settings. This is a tuple of hard and soft time limit value (int/float or None for no limit).

    Example value specifying a soft time limit of 3 seconds, and a hard time limt of 10 seconds:

    {'timelimit': (3.0, 10.0)}

Example message

This is an example invocation of the celery.task.PingTask task in JSON format:

{"id": "4cc7438e-afd4-4f8f-a2f3-f46567e7ca77",
 "task": "celery.task.PingTask",
 "args": [],
 "kwargs": {},
 "retries": 0,
 "eta": "2009-11-17T12:30:56.527191"}


Several types of serialization formats are supported using the content_type message header.

The MIME-types supported by default are shown in the following table.

Scheme MIME Type
json application/json
yaml application/x-yaml
pickle application/x-python-serialize
msgpack application/x-msgpack

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