Help-header is an express middleware module that adds Link headers to responses matching configured status codes. It is useful for linking error responses to your documentation to aid your API consumers in diagnosing errors. For example:

$ curl -i https://api.example.com/authorized_resource
HTTP/2 401
Content-Type: application/json; charset=utf-8
...
Link: <https://example.com/docs/authorization>; rel="help"
...

The package (with types) is available on npm. Install with npm install:

$ npm install help-header

See express documentation for how to install middleware.

A configuration object must be provided which tells help-header what status codes to match and what URLs to link to. URLs can be linked by any combination of status family and code. When processing a response, help-header first tries to match by status code, then by family. So for example, to link all 4XX response to general documentation and 403 status codes specifically to your authorization documentation, you may use something like:

const express = require('express');
const helpHeader = require('help-header').helpHeader;

const app = express();
app.use(
  helpHeader({
    401: "http://example.com/docs/authorization",
    clientError: "http://example.com/docs",
  })
);

The keys in the config object must be a number or one of:

• informational
• successful
• redirection
• clientError
• serverError

The values must be strings encoding valid URLs or URL objects.