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This middleware normalizes HTTP header names. By default, it normalizes to lowercase. It can also normalize to canonical form.

API Gateway does not perform any normalization, so without this middleware headers are propagated to Lambda exactly as they were sent by the client. Headers names are case insensitive, so normalization allows code reading header values to be simplified.

Other middlewares like jsonBodyParser or urlEncodeBodyParser will rely on headers to be one of the normalized formats, so if you want to support non-normalized headers in your app you have to use this middleware before those ones.

This middleware will copy the original headers in event.rawHeaders.


To install this middleware you can use NPM:

npm install --save @middy/http-header-normalizer


  • canonical (bool) (optional): if true, modifies the headers to canonical format, otherwise the headers are normalized to lowercase (default false)
  • defaultHeaders (object) (optional): Default headers to used if any are missing. i.e. Content-Type (default {})
  • normalizeHeaderKey (function) (optional): a function that accepts an header name as a parameter and returns its canonical representation.

Sample usage

import middy from '@middy/core'
import httpHeaderNormalizer from '@middy/http-header-normalizer'

const lambdaHandler = (event, context) => {
return {}

export const handler = middy()