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HTTP security headers check with grade (free)

web_security_headers
Read-onlyIdempotent

Check one URL's HTTP response headers for security misconfigurations, returning a weighted score and grade for quick security posture assessment.

Instructions

Check HTTP security response headers of one URL: Strict-Transport-Security (>=180 days), Content-Security-Policy (flags unsafe-inline/unsafe-eval), X-Content-Type-Options (nosniff), X-Frame-Options (or CSP frame-ancestors), Referrer-Policy, Permissions-Policy, Cross-Origin-Opener-Policy; plus information-disclosure headers (Server, X-Powered-By). Weighted score 0-100 and grade A-F (non-HTTPS capped at 40). WHEN TO USE: quick security posture / hygiene check of a site. Not a vulnerability scanner. Fetching: read-only GETs from this server with User-Agent "FairqueryBot ... Fairquery-MCP", 15 s timeout per request, body capped (1.5 MB HTML), max 5 redirects; URLs resolving to private/loopback/link-local addresses are refused (SSRF guard). Free, no token, no JavaScript rendering. One request (after redirects); headers are taken from the final response. RETURNS: one "security_headers" object: input, final_url, status_code, https, score, grade, headers[{header, present, value, warning, weight}], missing[], info_disclosure_headers[{header, value}], checked_at. Errors (isError=true, JSON {error, message, retryable}): INVALID_URL, BLOCKED_PRIVATE_ADDRESS, DNS_FAILED, FETCH_FAILED, TIMEOUT, TOO_MANY_REDIRECTS. WHEN NOT TO USE: not a vulnerability/penetration scan; for dependency CVEs use an OSV tool; for SEO use web_seo_audit. COST: free - runs locally in this MCP server (direct HTTP GETs), no APIFY_TOKEN, no Apify billing. EXAMPLE: {"url":"github.com"} -> {type:"security_headers", score:0-100, grade:"A".."F", missing:[...], ...}

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
urlYesRequired. One public domain or http(s) URL, e.g. "vercel.com" or "https://www.python.org/about/". Bare domains are fetched over https; private/loopback hosts are refused.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Addedv1.2.1

TDQS

A4.6/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Goes well beyond the readOnly/openWorld/idempotent annotations by disclosing the User-Agent, 15 s per-request timeout, 1.5 MB body cap, 5-redirect limit, single-request semantics, and an SSRF guard refusing private/loopback/link-local addresses. This is exactly the kind of operational context annotations cannot carry.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with purpose, then cleanly sectioned (WHEN TO USE / Fetching / RETURNS / WHEN NOT TO USE / COST / EXAMPLE). Some redundancy: COST restates 'free' already implied earlier, and 'not a vulnerability scanner' appears twice, so it is slightly longer than strictly necessary.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description fully specifies the return shape ('security_headers' object with headers, missing, info_disclosure_headers, score, grade, checked_at) and enumerates every error code (INVALID_URL, BLOCKED_PRIVATE_ADDRESS, DNS_FAILED, etc.). Nothing an agent needs to call or interpret results is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and the single 'url' parameter is already documented in the schema (examples, bare-domain-over-https, private-host refusal). The description's EXAMPLE adds marginal framing but no new parameter meaning, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource ('Check HTTP security response headers of one URL') and enumerates exactly which headers are evaluated and the scoring model (0-100, grade A-F). It is immediately distinguishable from siblings like web_seo_audit and any OSV/dependency tool.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives an explicit WHEN TO USE ('quick security posture / hygiene check'), an explicit WHEN NOT TO USE ('not a vulnerability/penetration scan'), and names concrete alternatives (OSV tools for CVEs, web_seo_audit for SEO). Routing is unambiguous.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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