Hookwarden — Webhook Integrity

The first MCP server doing webhook signature verification.
Local. Deterministic. Zero network. JS / TS / Python / PHP / Go — 27 providers — 3-state verdicts.

What it does

@hookwarden/mcp exposes hookwarden's deterministic webhook-verification engine as MCP tools. AI coding agents — Claude Desktop, Cursor, Continue, and apps built on the Anthropic Agent SDK — get two tools:

• scan_handler — scan pasted webhook handler code and get back a structured finding (verified / not-verified / manual-review) for Stripe, GitHub, Shopify, Twilio, and 23 other providers.
• verify_audit_chain — verify a hookwarden evidence pack's hash chain + KMS-signed Merkle roots offline (no network, no auth), returning { valid, broken_at_row, signatures_verified }.

Runs entirely client-side. Zero network egress from the MCP process. Zero auth. The same engine the hookwarden CLI ships — same rule pack, same content hashes, end-to-end provenance.

Install in one command

npx @hookwarden/mcp init

That command detects your installed MCP clients (Claude Desktop / Cursor / Continue), prints a per-OS summary table, and writes the canonical config to each one. .bak files land alongside every config it touches. Restart the relevant client and scan_handler + verify_audit_chain appear in the tool list.

Pass --all for non-interactive use, --dry-run to preview, --force to overwrite an existing mcpServers.hookwarden entry, or --clients claude-desktop,cursor to limit the set.

Manual configuration

If you'd rather not run the init helper, write the config by hand.

Claude Desktop

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "hookwarden": {
      "command": "npx",
      "args": ["-y", "@hookwarden/mcp"]
    }
  }
}

Cursor

~/.cursor/mcp.json — same shape as Claude Desktop:

{
  "mcpServers": {
    "hookwarden": {
      "command": "npx",
      "args": ["-y", "@hookwarden/mcp"]
    }
  }
}

Continue.dev

Continue uses a per-server file. Write ~/.continue/mcpServers/hookwarden.yaml:

name: hookwarden
command: npx
args: [-y, "@hookwarden/mcp"]

Anthropic Agent SDK

The Agent SDK is programmatic — there's no config file to edit. Drop this into your code:

import { query } from "@anthropic-ai/claude-agent-sdk";

for await (const message of query({
  prompt: "Audit this webhook handler for missing signature verification...",
  options: {
    mcpServers: {
      hookwarden: {
        command: "npx",
        args: ["-y", "@hookwarden/mcp"],
      },
    },
  },
})) {
  console.log(message);
}

The init helper does not write here — the SDK integration is code, not config.

The scan_handler tool

Inputs

Field	Type	Notes
code	string	Single-blob mode. Defaults to TypeScript; override with language. Mutually exclusive with files.
files	Record<string, string>	Multi-file mode. Keys are virtual file paths; language inferred from extension.
language	"js" | "ts" | "python"	Optional. "php" returns language_not_in_preview — PHP support ships in v0.8.1.
provider	string	Optional. Case-insensitive ("stripe" = "Stripe"). unknown_provider if not in the rule pack.

Output

Returns Tool.result with structuredContent first-class (MCP spec 2025-06-18) plus a companion stringified-JSON text block for backwards compatibility:

{
  "verdict_summary": { "verified": 0, "not_verified": 1, "manual_review": 0, "parse_error": 0 },
  "findings": [
    {
      "rule_id": "stripe/missing-signature-verification",
      "provider": "stripe",
      "severity": "critical",
      "verdict": "not-verified",
      "file": "__handler.ts",
      "line_start": 7,
      "line_end": 9,
      "message": "Webhook handler reads req.body without calling stripe.webhooks.constructEvent...",
      "provider_docs_url": "https://stripe.com/docs/webhooks",
      "references": [
        "https://www.svix.com/blog/common-failure-modes-for-webhook-signatures/",
        "https://hookdeck.com/webhooks/guides/webhook-security-vulnerabilities-guide"
      ],
      "rule_pack_version": "0.7.2"
    }
  ],
  "scan_metadata": {
    "engine_version": "0.7.2",
    "rule_pack_version": "0.7.2",
    "rule_pack_content_hash": "938f7565e29f19e0cbd34594731d1de2b0ffd40ee87aacaa8be2435fc1f47f32"
  }
}

Verdict vocabulary

Verdict	Meaning
verified	Engine proved the handler verifies signatures via the provider's documented SDK call.
not-verified	Engine proved the handler does NOT verify signatures (or verifies after side effects).
manual-review	Engine has structural evidence but can't decide without human eyes — review the snippet.

Same 3-state vocabulary as the CLI. No remapping in the MCP layer.

Error payloads (isError: true)

Error	Trigger
empty_input	Neither code nor files provided.
exclusive_input_modes	Both code and files provided — pick one.
language_not_in_preview	language: "php" — PHP ships in v0.8.1. Suggestion: npx hookwarden scan.
unsupported_language	language outside the known set.
unknown_provider	provider not in the rule pack. Response includes the sorted known list.
engine_drift / rules_drift	Boot or call-time drift — see drift-detection.

Parse failures don't crash the transport — they emit as rule_id: "engine/parse-error" findings with severity high and increment verdict_summary.parse_error.

The verify_audit_chain tool

Verify a hookwarden evidence pack's integrity offline — no network, no AWS, no credentials. "Verify the chain without trusting hookwarden." The tool walks the per-row hash chain, roundtrips the manifest hash, and — for v1.1 packs that embed the signing CMK's SPKI public key — verifies the ECDSA-P256 (MessageType:DIGEST) Merkle-root + manifest signatures with node:crypto.

Inputs

Field	Type	Notes
evidence_pack_json	string	The full evidence-pack JSON (the file hookwarden's evidence export produces). Both v1.0 and v1.1 packs are accepted.

Output

{
  "valid": true,
  "broken_at_row": null,
  "signatures_verified": 2
}

Field	Meaning
valid	true iff the hash chain is intact AND the manifest hash roundtrips AND every signature that could be verified offline verified.
broken_at_row	The seq of the first row whose chain hash didn't match, or null if the chain is intact. Signature validity is independent of chain integrity.
signatures_verified	Count of offline-verified signatures: N Merkle-root signatures + 1 manifest signature (N+1). 0 for v1.0 packs (no embedded public key) — the tool emits a signatures not verifiable offline (v1.0 pack) note instead of failing.

Trust model

The v1.1 pack carries its own SPKI public key. The signature proves the pack was not altered after signing by the holder of that key — it is trust-on-first-use. To pin trust to a specific signer out-of-band, an auditor can cross-check signature.signing_cmk_arn against AWS KMS GetPublicKey and confirm the embedded SPKI key matches. Malformed pack JSON returns isError: true (error: "invalid_pack_json") — the tool never throws past its boundary.

This tool imports only @hookwarden/canonical-json (the shared RFC 8785 byte-equality anchor) + node:crypto. It does not load the engine or rule pack and does not run the drift gate.

Integrity claims

• Zero outbound TCP — the published tarball passes pnpm inspect-bundle, a structural CI gate that rejects any source-file import of HTTP clients (node:http, axios, undici, etc.) and any direct dependency outside the documented allowlist.
• Drift detection — every scan_handler call cross-checks the runtime-resolved engine + rule-pack hashes against the build-time dist/build-manifest.json. Mismatch returns isError: true with structured engine_drift / rules_drift payload. No env-var opt-out. See drift-detection — including the v0.8.0 engine-content-hash limitation.
• No telemetry — the tarball declares no analytics or tracking SDKs (@datadog/*, @segment/*, @sentry/*, etc.) in dependencies or transitively in source-file imports.
• Open source — Apache-2.0 at Hookwarden/hookwarden/packages/mcp/. Engine + rule pack land in the same monorepo and ship under the same license.

Links

• Documentation — getting started, tool surface reference, drift detection
• npm package
• GitHub repository
• Apache-2.0 License

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Copyright 2026 Hookwarden contributors. Apache License 2.0.