c2pa-mcp

An MCP server that verifies C2PA Content Credentials and returns an LLM-ready verdict.

Point any MCP client (Claude Desktop, Claude Code, Cursor, ...) at a local file or a URL and get back a plain-language answer: is this image/video/audio trusted, valid, tampered, or unsigned? Who signed it? Is it AI-generated? What's its edit history and provenance lineage?

Built by c2paviewer.com. Verification runs locally on the official C2PA Rust engine via @contentauth/c2pa-node. Files never leave your machine.

Read-only. This server verifies and inspects Content Credentials. It does not sign or create them.

Install

No global install needed. Add it to your MCP client config and it runs via npx:

{
  "mcpServers": {
    "c2pa": {
      "command": "npx",
      "args": ["-y", "@c2paviewer/c2pa-mcp"]
    }
  }
}

• Claude Desktop: Settings → Developer → Edit Config, add the block above.
• Claude Code: claude mcp add c2pa -- npx -y @c2paviewer/c2pa-mcp
• Cursor / others: add the same mcpServers entry to the client's MCP config.

Requires Node.js 22+ (the @contentauth/c2pa-node engine requires it).

First run: the underlying engine (@contentauth/c2pa-node) downloads a ~18MB native binary on first install. On a slow connection this can outlast an MCP client's startup timeout — if the very first launch seems to hang, let the download finish and relaunch; subsequent runs are instant.

Tools

| Tool | What it does | |------|--------------| | verify_c2pa_file | Verify a local image/video/audio/PDF by path. | | verify_c2pa_url | Download a public https media URL and verify it (SSRF-guarded). | | scan_c2pa_directory | Audit a folder: which files have credentials, their verdict, signer, AI status. | | c2pa_info | Report engine version, supported media types, and trust-list status. |

Each verify tool returns a human-readable summary plus a structured digest:

{
  "verdict": "valid_untrusted",    // trusted | valid_untrusted | valid_trust_unknown | invalid | no_credentials | error
  "summary": "Content Credentials are cryptographically valid, but the signer ... 1 earlier version in its provenance chain failed validation; this file's own signature is unaffected.",
  "signer": { "name": "Example Signer", "trusted": false },
  "aiGenerated": { "isAI": true, "tools": ["DALL-E"], "digitalSourceTypes": ["...trainedAlgorithmicMedia"] },
  "provenance": [
    { "depth": 0, "title": "This file", "relationship": "This file", "verdict": "valid", "manifestLabel": "urn:...", "issues": [] },
    { "depth": 1, "title": "source.jpg", "relationship": "Edited from", "verdict": "invalid", "manifestLabel": "urn:...",
      "issues": [ { "code": "claimSignature.mismatch", "severity": "error", "explanation": "..." } ] }
  ],
  "edits": [ { "label": "Created", "agent": "Photoshop", "when": "...", "detail": "" } ],
  "watermarks": [ { "kind": "synthid", "assertionLabel": "...", "algorithm": "" } ],
  "issues": [ { "code": "signingCredential.untrusted", "severity": "warning",   // THIS file's own problems (plus whatever drove an Invalid verdict)
               "explanation": "The signature is cryptographically valid, but ..." } ],
  "ingredientIssues": [                                                           // problems on earlier versions in the chain
    { "ingredientTitle": "source.jpg", "manifestLabel": "urn:...", "worstSeverity": "error",
      "codes": [ { "code": "claimSignature.mismatch", "severity": "error", "explanation": "..." } ] }
  ],
  "trust": { "evaluated": true, "partial": false, "listSource": "https://.../C2PA-TRUST-LIST.pem, ..." }
}

Provenance chain vs. the file itself

issues and verdict describe the active manifest — this file's own signature and content. Problems found on ingredients (earlier versions or components the file was made from) are reported separately in ingredientIssues and on the matching provenance[].issues, and never change the file's verdict. This follows C2PA 2.2 §15.11 (a validator must report a failing ingredient, but the active manifest keeps its own result) and matches what CAI Verify shows. So a file re-signed from a tampered original can legitimately be trusted while its lineage shows an invalid node — the model should read both.

Pass "includeRaw": true to also get the full raw manifest store.

Trust list

To report a signer as trusted (not just cryptographically valid), the server checks the signing certificate against the same five trust inputs c2paviewer.com uses, fetched live and cached (24h TTL) so decisions stay current without a release:

Official C2PA Conformance Program (going-forward signers)

• C2PA-TRUST-LIST.pem — CA anchors for claim signers
• C2PA-TSA-TRUST-LIST.pem — CA anchors for Time-Stamp Authorities (folded into the same anchor bundle; without it valid files can carry timeStamp.untrusted)

CAI Interim Trust List (frozen Jan 2026, officially temporary, but still the only thing that recognizes pre-conformance signers — Adobe, Leica, Truepic, Canon, Samsung, Fastly, and most real-world content today)

• anchors.pem — legacy CA anchors
• allowed.sha256.txt — allow-list of specific end-entity certificate hashes; a signer whose leaf cert is listed is trusted even when nothing chains to an anchor
• store.cfg — accepted Extended Key Usage OIDs

Without the interim group, mainstream signed content reads as valid_untrusted.

If an input can't be fetched, the server degrades loudly: with at least one anchor list loaded it still evaluates trust but sets trust.partial: true and names the missing input in trust.reason (signers recognized only by that input will read as untrusted); with no anchors at all the verdict becomes valid_trust_unknown and trust.evaluated is false. It never silently treats an unknown signer as trusted, and never silently uses a stale snapshot.

Environment overrides:

| Variable | Default | Purpose | |----------|---------|---------| | C2PA_TRUST_LIST_URL | conformance + TSA + ITL anchors | Comma-separated PEM URLs. Replaces the default anchor set. | | C2PA_TRUST_ALLOWED_LIST_URL | CAI allowed.sha256.txt | End-entity allow-list URL. Set to an empty string to disable. | | C2PA_TRUST_CONFIG_URL | CAI store.cfg | EKU config URL. Set to an empty string to disable. | | C2PA_TRUST_TTL_SECONDS | 86400 | Cache lifetime for the fetched trust list. | | C2PA_MAX_FETCH_BYTES | 104857600 | Max download size for verify_c2pa_url (100 MB). | | C2PA_MAX_FILE_BYTES | 524288000 | Max size of a local file the file/scan tools will verify (500 MB). | | C2PA_ALLOWED_ROOTS | (unset) | Comma/semicolon-separated absolute paths. When set, verify_c2pa_file and scan_c2pa_directory refuse any path outside these roots. |

Security

• Local processing. Files are read and verified on your machine; nothing is uploaded.
• SSRF-guarded URL fetching. verify_c2pa_url allows only public https, pins the resolved IP against DNS rebinding, re-validates every redirect, sends no cookies or auth, and enforces a content-type allowlist plus size cap.
• Local path safety. The file/scan tools reject remote file:// and UNC paths, resolve symlinks before the allowed-roots check, and return a generic error for inaccessible paths.
• Set C2PA_ALLOWED_ROOTS in any untrusted context. The file/scan tools expose the host filesystem by design, so a prompt-injected model could point them anywhere. Confining them to a specific directory is the single most important hardening setting.
• Trust integrity. Trust lists are fetched over HTTPS (integrity rests on TLS and the upstream sources); the cache is per-user (0700/0600, ownership-checked) and bound to the configured URL set.

Limitations

• Experimental. Not legal evidence. C2PA tooling and trust infrastructure are still evolving. Do not rely on these verdicts for legal, compliance, or safety-critical decisions.
• Watermarks are reported as declared, not pixel-verified. A synthid entry means the manifest declares a SynthID watermark; confirming the signal in the pixels requires the vendor's detector.
• AI-generation reflects what the manifest declares via IPTC digitalSourceType. Absence of an AI declaration is not proof the content is not AI-generated.

Troubleshooting

• Every verification fails with "Verification engine failed to load". The native @contentauth/c2pa-node binary was interrupted or corrupted during install (common on slow/unreliable connections). Run c2pa_info — it reports engine: FAILED: <reason> when this happens. Fix: reinstall the dependency (delete node_modules/@contentauth/c2pa-node and reinstall, or npm cache clean --force then re-run). Checksum/retry hardening of that download lives in the upstream @contentauth/c2pa-node postinstall script, which this project doesn't control.
• verify_c2pa_url fails with "timed out after ...ms". The fetch exceeded C2PA_FETCH_TIMEOUT_MS (default 30000). Raise it if you're verifying URLs from a slow host.

Development

npm install
npm run build
npm test          # builds, then runs unit + end-to-end tests (network needed for the trust list)

License

Source code is dual-licensed under MIT or Apache-2.0, at your option.

The test images under test/fixtures/ are redistributed unmodified from c2pa-org/public-testfiles and are licensed separately under CC BY-SA 4.0.

Note: if you publish under an unscoped name instead of @c2paviewer/c2pa-mcp, change name in package.json and the args in the install block above; nothing else depends on the package name.