Command Line Interface

The run_lambda package also offers a command-line tool for running Lambda functions:

$ run_lambda path/to/ path/to/event.json

Installing the run_lambda package from the Python Package Index (i.e. via pip) should automatically add the tool to your path. For information on how to use the tool, run run_lambda --help:

$ run_lambda --help
usage: run_lambda [-h] [-f HANDLER_FUNCTION] [-t TIMEOUT]
                  [-c CONTEXT_FILENAME]
                  filename event

Run AWS Lambda function locally

positional arguments:
  filename              name of file containing Lambda function
  event                 name of file containing JSON event data

optional arguments:
  -h, --help            show this help message and exit
                        Name of handler function. Defaults to "handler"
  -t TIMEOUT, --timeout TIMEOUT
                        Timeout (in seconds) for function call. If not
                        provided, no timeout will be used.
                        Filename of file containing JSON context data

Context JSON

The context JSON data can include the following fields:

  "aws_request_id": "bf77967d-c53a-5659-9d91-2417e2a3ee58",
  "client_context": {
    "client": {
      "app_package_name": null,
      "app_title": null,
      "app_version_code": null,
      "app_version_name": null,
      "installation_id": null
    "custom": {},
    "env": {}
  "function_name": "my_lambda",
  "function_version": "$LATEST",
  "identity": {
    "cognito_identity_id": null,
    "cognito_identity_pool_id": null
  "invoked_function_arn": "arn:aws:lambda:region-1:813876719243:function:my_lambda",
  "log_group_name": "/aws/lambda/my_lambda",
  "log_stream_name": "2016/12/11/[$LATEST]6ac39f0272c07aa3cd548e6d5a9e8881",
  "memory_limit_in_mb": 128

Any fields that are not present in the provided context JSON will be populated with default values. Any invalid fields (i.e. any fields other than the ones listed above) are ignored.

To generate a template context data JSON file like the one shown above, use the run_lambda_context_template command. For information on how to use the command, run run_lambda_context_template --help:

$ run_lambda_context_template --help
usage: run_lambda_context_template [-h] [-o OUTPUT_FILENAME]

Generate a template context JSON file

optional arguments:
  -h, --help          show this help message and exit
  -o OUTPUT_FILENAME  output file for template, prints to stdout if omitted