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Witnessd

Witness public URLs and API responses, archive snapshots, and verify signed, Merkle-anchored evidence.

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Install Witnessd

Pick your client, then add it in one click or paste the config.

STDIONode.js
~/Library/Application Support/Claude/claude_desktop_config.json
claude_desktop_config.json
{
  "mcpServers": {
    "witnessd": {
      "command": "npx",
      "args": [
        "-y",
        "witnessd-mcp"
      ],
      "env": {
        "EVM_PRIVATE_KEY": "YOUR_VALUE_HERE",
        "WITNESSD_API_KEY": "YOUR_VALUE_HERE",
        "WITNESSD_URL": "YOUR_VALUE_HERE"
      }
    }
  }
}

Settings → Developer → Edit Config, merge this into mcpServers, then fully quit and reopen Claude Desktop.

Values are written into the snippet above so you can paste it as is. They never leave your browser.

Install not yet sandbox-tested— the server itself is confirmed live (we called its tools/list endpoint). The stdio install command is a separate, ongoing check.

Overview

witnessd MCP server lets agents independently fetch public URLs or API endpoints and preserve tamper-evident evidence of their responses. Its tools create snapshots, return signed certificates, retrieve archived response bodies, and expose Merkle proofs with Base anchor details. Use it before transactions, decisions based on third-party data, or disputes about what an endpoint showed at a specific time. Paid calls use USDC on Base through x402 or a prepaid witnessd credit key.

Use cases

  • Witness a seller’s published price or terms before transacting
  • Record the response returned by a third-party API before acting on it
  • Retrieve archived evidence for an existing snapshot ID
  • Verify a signed certificate and its Base-anchored Merkle proof

Key features

  • Independent URL and API response witnessing
  • Signed certificates with Ed25519 signatures
  • Hourly Merkle batching anchored on Base
  • Archived response retrieval as base64
  • x402 USDC payments or prepaid API credits

Tools3

What Witnessd lets your agent do. Expand a tool for its parameters.

Verified live~358 tokens of context

Security & health

What it can reach and how reliably it runs — from our own checks, not the maintainer’s claims.

ActiveLast checked Today

Recent health check succeeded.

10/10 checks healthy over the last 57d

What it can do

From the 3 tools this server returned when we ran it.

Makes network requests · 2Read-only tools · 3
Network at startup3 connections
Files written at startupNone
Install scriptsNone
npm provenanceNot published
Package age70 days
Maintainers1

Observed 2026-10-24 in an isolated sandbox. A description of reach, not a security audit.

Supply-chain signal

No high-severity advisories surfaced by our automated scan.

Critical 0High 0Medium 0Low 0

Scanned 2d ago via OSV.dev · witnessd-mcp (npm)

Adoption & maintenance

Factual signals from GitHub, npm, and our automated checks — not a rating.

npm downloads138Package downloads in the last 30 days.
Last commit8d agoMost recent push to the default branch.
Tools exposed3Callable tools this server registers over MCP.
Directory activity1 viewsConfig copies, upvotes, and views on AllMCPs.

How Witnessd works

What witnessd MCP server does

witnessd MCP server gives an MCP-compatible agent a neutral way to record what a public web page or API endpoint returned at a particular time. The service fetches the target independently, hashes the response, timestamps the snapshot, archives it, and issues a signed certificate. This creates evidence for situations where the content may later change, such as published prices, terms, or third-party data used in a transaction.

The service is limited to content available to an unauthenticated stranger. It does not access logged-in resources or private networks, and response bodies are limited to 10 MB. Certificates expose hashes, timestamps, and verification data publicly, while archived content is delivered to paying requesters rather than republished.

How it works

Call witness_url with a URL or API endpoint to create a snapshot. The response includes a snapshot ID and signed certificate. Snapshot hashes are combined into hourly Merkle batches and anchored on Base. A certificate contains the manifest, Ed25519 signature, Merkle inclusion proof, and Base anchor transaction once the batch is anchored.

Anyone can independently verify the certificate. The documented verification process derives a leaf hash from the canonical JSON manifest, checks the Ed25519 signature, validates the Merkle proof, and checks the Base anchor. A standalone verifier is available at witnessd.vip/verify.js.

Setup and configuration

Run the server with:

Terminal
npx -y witnessd-mcp

Configure an MCP client to launch the command with npx, the -y and witnessd-mcp arguments, and payment credentials in its environment. Set one payment option:

  • EVM_PRIVATE_KEY: a wallet key holding USDC on Base. Calls are paid automatically through x402; the buyer signs payments and does not need ETH for gas.
  • WITNESSD_API_KEY: a prepaid credit key purchased from the witnessd credits endpoint.

Use a dedicated wallet for EVM_PRIVATE_KEY rather than a primary wallet. WITNESSD_URL can point the server at another witnessd instance; the default is https://witnessd.vip.

Claude Code can install the plugin and skill through its marketplace. Agents that support Agent Skills can add the repository with npx skills add jschunter/witnessd-mcp; running npx -y witnessd-mcp provides the MCP server without the skill.

Tools and capabilities

  • witness_url costs $0.02 and independently fetches, hashes, timestamps, and archives a URL or API response. It returns the snapshot ID and signed certificate.
  • get_certificate is free and returns certificate data for any snapshot ID, including the manifest, signature, Merkle proof, and Base anchor transaction when available.
  • retrieve_snapshot costs $0.05 and returns the archived response body as base64 together with its certificate. It can retrieve snapshots created by other parties, allowing a requester to obtain evidence for an existing snapshot.

Limitations and notes

Certificates are public, so their hashes, timestamps, and proofs can be inspected by others. Archived response content is restricted to paying requesters. The service witnesses only publicly accessible responses and cannot establish what a private or authenticated endpoint returned. The skill bundled with the repository recommends no more than five paid calls per task without approval, reporting each call in one line, and avoiding paid retry loops.

The project is licensed under MIT.

Read the full README View source on GitHub

Reviews

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Frequently Asked Questions about Witnessd

witnessd is an MCP server that connects agents to the witnessd public-web witnessing service. Its main tools fetch and archive a URL or API response, return a signed certificate, retrieve certificates by snapshot ID, and recover archived response bodies for paid requests. Certificates include verification data for independent checking.

Install it with `npx -y witnessd-mcp` and add that command to your MCP client configuration. The server accepts payment credentials through the environment. Claude Code can install the repository plugin, while Agent Skills-compatible agents can use `npx skills add jschunter/witnessd-mcp`.

Verify a snapshot by checking its manifest, Ed25519 signature, Merkle inclusion proof, and Base anchor transaction. The leaf hash is derived from the canonical JSON manifest, and a standalone checker is available at `witnessd.vip/verify.js`.

Pay with either `EVM_PRIVATE_KEY` for automatic USDC payments on Base through x402 or `WITNESSD_API_KEY` for prepaid credits. `witness_url` costs $0.02 and `retrieve_snapshot` costs $0.05; `get_certificate` is free.

Yes. `retrieve_snapshot` works with any snapshot ID, including snapshots witnessed by other parties, and returns the archived response body plus certificate to the paying requester.

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