This document describes Celery 2.3. 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 (introduced after v2.0.2)

    string (ISO 8601)

    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_id

    The taskset this task is part of.

  • chord

    Siginifies 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.

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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