Ready to take your JavaScript development to the next level? Meet npm Enterprise - the ultimate in enterprise JavaScript.Learn more »


1.6.2 • Public • Published



Build Status Known Vulnerabilities

Lambda-local lets you test Amazon Lambda functions on your local machine, by providing a simplisitc API and command-line tool.

The context of the Lambda function is already loaded so you do not have to worry about it. The calls are fully customizable, as you can pass any event (JSON) object to any handler function.


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: Definitions

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 sampled from what's visible when running an actual Lambda function on AWS, and the available documentation 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 or -P options (or their API counterpart) with the aws credentials file. More infos here:

About: CLI

Available Arguments

  • -l, --lambda-path <lambda index path> (required) Specify Lambda function file name.
  • -e, --event-path <event path> (required) Specify event data file name.
  • -h, --handler <handler name> (optional) Lambda function handler name. Default is "handler".
  • -t, --timeout <timeout> (optional) Seconds until lambda function timeout. Default is 3 seconds.
  • -r, --region <aws region> (optional) Sets the AWS region, defaults to us-east-1.
  • -P, --profile-path <aws profile name> (optional) Read the specified AWS credentials file.
  • -p, --profile <aws profile name> (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] (optional) Starts lambda-local using the NodeJS inspector (available in nodejs > 8.0.0)

About: API


API accessible with:

const lambdaLocal = require("lambda-local");


Executes a lambda given the options object, which is a dictionary where the keys may be:

  • 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)



Those functions allow to access the winston logger used by lambda-local.

API examples

A lot of examples, especially used among Mocha, may be found in the test files over: here

Basic usage: 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) {

Basic usage: using callbacks

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'})

Other links


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


This library is released under the MIT license.


npm i lambda-local

Downloadsweekly downloads









last publish


  • avatar
  • avatar
Report a vulnerability