# MCP Tool Surface Digest & Attestation

> MCP Tool Surface Digest & Attestation is a paid API for AI agents from witness.holoweave.org, paid per call via x402, $0.01/call, status down (last checked 2026-09-15).

Computes a stable, signed digest over an MCP server's tools/list (tool names, descriptions, and inputSchemas) and returns a cryptographically signed attestation as a baseline for future integrity comparisons.

## Facts

- Endpoint: POST https://witness.holoweave.org/v1/mcp-digest
- Price: $0.01/call
- Payment: x402
- Status: down
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/mcp-tool-surface-digest-attestation-aae653a4
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_fTsSEVndtqLqoxt4_O4J6

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 mcp-tool-surface-digest-attestation-aae653a4 -d '<json body>'
```

Example prompt: Take the tools/list from my MCP server and compute a signed digest of the whole tool surface — names, descriptions, and schemas — so I have a pinned attestation I can compare against later if I suspect something changed.

## When to prefer this

Use this endpoint when you need a cryptographically signed, tamper-evident snapshot of an MCP server's tool surface at a point in time — especially before deployment, before and after updates, or when establishing a baseline for ongoing drift detection. Prefer this over the companion drift-detection endpoint when you want to CREATE the baseline rather than compare against one. Choose this over ad-hoc hashing because the ed25519 attestation is independently verifiable and externally signed.

## Known failure modes

- Empty or malformed tools array returns an error or digest with tool_count 0
- Missing required 'name' field on any tool item causes a validation error
- Network/payment failure (x402 micropayment not completed) blocks the response
- Malformed inputSchema objects may be excluded or cause serialization errors
- If the signing key is rotated, old attestations will reference a deprecated key_id

## How this service works

Web bot auth debugging for AI agents, priced per check at $0.01. RFC 7638 keyid thumbprint verification, RFC 9421 Ed25519 signature verification, and per-verifier acceptance rules. Signed attestations, published fixtures, sources with dates.

## Output

Returns a JSON object containing an ed25519-signed attestation with a verdict ('pass'), the overall surface_digest (sha256 over all tools), per-tool digests keyed by tool name, the tool count, and a key_id identifying the signing key. This signed attestation can be stored as a trusted baseline and compared against future snapshots to detect drift or tampering.

## Response schema (JSON Schema)

```json
{
 "example": {
  "signature": {
   "alg": "ed25519",
   "value": "base64...",
   "key_id": "aw-attest-2026-08"
  },
  "attestation": {
   "verdict": "pass",
   "endpoint": "mcp-digest",
   "evidence": {
    "tools": {
     "search": "3ac1…"
    },
    "digest_alg": "sha256",
    "tool_count": 1,
    "surface_digest": "9f2b…"
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/mcp-tool-surface-digest-attestation-aae653a4/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from witness.holoweave.org](https://www.zero.xyz/host/witness.holoweave.org/llms.txt)