# Dev Reference – HTTP Header Lookup

> Dev Reference – HTTP Header Lookup is a paid API for AI agents from dev-reference.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-29).

Returns the purpose, direction (request/response), security notes, and IANA registration status for a named HTTP header field.

## Facts

- Endpoint: GET https://dev-reference.x402tookit.com/http-header?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/dev-reference-http-header-lookup-3bf34029
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_d_WXdYyPGbrT4fACE8d5M

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability dev-reference-http-header-lookup-3bf34029
```

Example prompt: What does the Strict-Transport-Security HTTP header do — is it a request or response header, what's its purpose, any security notes, and is it officially registered with IANA?

## When to prefer this

Use this endpoint when an agent or developer needs authoritative, structured information about a specific HTTP header — including its semantics, direction, security implications, and IANA registration status — rather than a free-text web search. Ideal for documentation generation, security audits, and developer tooling where structured, reliable metadata is required.

## Known failure modes

- Unknown or non-standard header name may return null fields or unregistered status
- Misspelled header name may produce empty or degraded result
- Very new or experimental headers may lack IANA registration data
- Network or upstream lookup failure may return a degraded flag with partial data

## How this service works

Explain an HTTP header: request or response, purpose, security notes, and its IANA registration status.

## Output

A structured record containing the header's canonical name, direction (request or response), a plain-English summary of its purpose, a security note highlighting any risks or best practices, its IANA registration status (boolean and registry status string), a reference URL, and metadata such as the data freshness date and whether the result is degraded.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "name"
     ],
     "properties": {
      "name": {
       "type": "string",
       "description": "Header field name, for example Strict-Transport-Security"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "name": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "purpose": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "direction": {
       "type": [
        "null",
        "string"
       ]
      },
      "reference": {
       "type": [
        "null",
        "string"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "notChecked": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "registered": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "securityNote": {
       "type": [
        "null",
        "string"
       ]
      },
      "registryStatus": {
       "type": [
        "null",
        "string"
       ]
      },
      "structuredType": {}
     }
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/dev-reference-http-header-lookup-3bf34029/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from dev-reference.x402tookit.com](https://www.zero.xyz/host/dev-reference.x402tookit.com/llms.txt)