For the complete documentation index, see llms.txt. Markdown versions of all docs pages are available by appending .md to any docs URL.

Header manipulation

Add, set, or remove HTTP request and response headers.

Attaches to:

There are a few different policies that offer manipulation of HTTP requests and responses.

The requestHeaderModifier and responseHeaderModifier modify request and response headers respectively. These allow you to add, set, or remove headers. add and set differ in the case the header already exists; set will replace it while add will append.

# yaml-language-server: $schema=https://agentgateway.dev/schema/config
mcp:
  port: 3000
  policies:
    requestHeaderModifier:
      add:
        x-req-added: value
      remove:
      - x-remove-me
  targets:
  - name: everything
    stdio:
      cmd: npx
      args: ["@modelcontextprotocol/server-everything"]

# yaml-language-server: $schema=https://agentgateway.dev/schema/config
binds:
- port: 3000
  listeners:
  - routes:
    - policies:
        requestHeaderModifier:
          add:
            x-req-added: value
          remove:
          - x-remove-me
      backends:
      - host: localhost:8080

More advanced operations are available with the transformation policy. Like the HeaderModifier policies, this can also add, set, or remove headers, but can also manipulate HTTP bodies. Additionally, each modification is based on a CEL expression rather than static strings.