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Lambda-local lets you test Amazon Lambda functions on your local machine with sample event data. The context of the Lambda function is already loaded so you do not have to worry about it. You can pass any event JSON object as you please.


npm install -g lambda-local


As a command line tool

You can use Lambda-local as a command line tool.

# Simple usage 
lambda-local -l index.js -h handler -e examples/s3-put.js
# Input environment variables 
lambda-local -l index.js -h handler -e examples/s3-put.js -E '{"key":"value","key2":"value2"}'

In another node.js script

You can also use Lambda local directly in a script. For instance, it is interesting in a MochaJS test suite in order to get test coverage.

See API for more infos

About: CLI


  • -l, --lambda-path (required) Specify Lambda function file name.
  • -e, --event-path (required) Specify event data file name.
  • -h, --handler (optional) Lambda function handler name. Default is "handler".
  • -t, --timeout (optional) Seconds until lambda function timeout. Default is 3 seconds.
  • -r, --region (optional) Sets the AWS region, defaults to us-east-1.
  • -P, --profile-path (optional) Read the specified AWS credentials file.
  • -p, --profile (optional) Use with -P: Read the AWS profile of the file.
  • -E, --environment <JSON {key:value}> (optional) Set extra environment variables for the lambda
  • --wait-empty-event-loop (optional) Sets callbackWaitsForEmptyEventLoop=True => will wait for an empty loop before returning. This is false by default because our implementation isn't perfect and only "emulates" it.
  • --envdestroy (optional) Destroy added environment on closing. Defaults to false
  • -v, --verboselevel <3/2/1/0>', (optional) Default 3. Level 2 dismiss handler() text, level 1 dismiss lambda-local text and level 0 dismiss also the result.
  • --envfile <path/to/env/file> (optional) Set extra environment variables from an env file
  • --inspect [host:]port Starts lambda-local using the NodeJS inspector (available in nodejs > 8.0.0)

Event data

Event sample data are placed in examples folder - feel free to use the files in here, or create your own event data. Event data are just JSON objects exported:

// Sample event data
module.exports = {
    foo: "bar"


The context object has been directly extracted from the source visible when running an actual Lambda function on AWS. They may change the internals of this object, and Lambda-local does not guarantee that this will always be up-to-date with the actual context object.


Since the Amazon Lambda can load the AWS-SDK npm without installation, Lambda-local has also packaged AWS-SDK in its dependencies. If you want to use this, please use the "-p" option with the aws credentials file. More infos here: http://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html#cli-config-files

About: API



Executes a lambda given the options object where keys are:

  • event - requested event as a json object
  • lambdaPath - requested path to the lambda function
  • lambdaFunc - pass the lambda function. You cannot use it at the same time as lambdaPath
  • profilePath - optional, path to your AWS credentials file
  • profileName - optional, aws profile name. Must be used with
  • lambdaHandler - optional handler name, default to handler
  • region - optional, AWS region, default to us-east-1
  • callbackWaitsForEmptyEventLoop - optional, default to false. Setting it to True will wait for an empty loop before returning.
  • timeoutMs - optional, timeout, default to 3000 ms
  • environment - optional, extra environment variables for the lambda
  • envfile - optional, load an environment file before booting
  • envdestroy - optional, destroy added environment on closing, default to false
  • verboseLevel - optional, default 3. Level 2 dismiss handler() text, level 1 dismiss lambda-local text and level 0 dismiss also the result.
  • callback - optional, lambda third parameter callback. When left out a Promise is returned
  • clientContext - optional, used to populated clientContext property of lambda second parameter (context)


If you are using winston, this pass a winston logger instead of the console.

Example Usage for API

Basic: In another node.js script

const lambdaLocal = require('lambda-local');
var jsonPayload = {
    'key': 1,
    'another_key': "Some text"
    event: jsonPayload,
    lambdaPath: path.join(__dirname, 'path_to_index.js'),
    profilePath: '~/.aws/credentials',
    profileName: 'default',
    timeoutMs: 3000,
    callback: function(err, data) {
        if (err) {
        } else {
    clientContext: JSON.stringify({clientId: 'xxxx'})
Using Promises
const lambdaLocal = require('lambda-local');
var jsonPayload = {
    'key': 1,
    'another_key': "Some text"
    event: jsonPayload,
    lambdaPath: path.join(__dirname, 'path_to_index.js'),
    profilePath: '~/.aws/credentials',
    profileName: 'default',
    timeoutMs: 3000
}).then(function(done) {
}).catch(function(err) {

Use lambda-local to Mock

You can use Lambda local to mock your lambda then run it, using MochaJS and SinonJS

In this sample, we assume that you got a test function like this:

 * Lambda function used to test mocking.
exports.getData = function getData(){
    return "WrongData";
exports.handler = function(event, context) {
    context.done(null, exports.getData()); 

Then you will be able to use in your test.js mocha file, something like:

    //An empty event
    var jsonPayload = {
    var done, err;
    before(function (cb) {
        var lambdalocal = require('lambda-local');
        var lambdaFunc = require("path_to_test-function.js");
        //For instance, this will replace the getData content
        //see on sinonjs page for more options
            event: jsonPayload,
            lambdaFunc: lambdaFunc, //We are directly passing the lambda function
            lambdaHandler: "handler",
            callbackWaitsForEmptyEventLoop: true,
            timeoutMs: 3000,
            callback: function (_err, _done) { //We are storing the results and finishing the before() call => one lambda local call for multiple tests
                err = _err;
                done = _done;
            verboseLevel: 1 //only prints a JSON of the final result
    describe("Your first test", function () {
        it("should return mocked value", function () {
            assert.equal(done, "MockedData");
    ... Other tests


  • Run make to install npm modules. (Required to develop & test lambda-local)
  • Run make test to execute the mocha test.


This library is released under the MIT license.


npm i lambda-local

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