# Serverless Functions

The dev server looks for "lambda functions" in the directory (default: ./api/src/functions) specified by your redwood.toml configuration file.

Each lambda function is mapped to a URI based on their filename, as an example: ./api/src/functions/graphql.js would be accessible at http://localhost:8911/graphql.

The ./api directory is watched for modifications, when they are detected the modules are reimported.

A lambda function must export a handler. You can execute the supplied callback function to return a response:

export const handler = (event, context, callback) => {
  return callback(null, { statusCode: 200, body: 'Hello, world' })
}