ProofCheck

Name: ProofCheck
Author: something-agent

by something-agentversion 0.1.0i★ –iRuns in the cloud

Registry nameio.github.something-agent/proofcheck

Install

Overview

Description from the maker (original English)

Free x402 offer/receipt checker: verifies signatures and whether the signer fits the host.

PopNx MCP’s three pillars

These three are never merged into one score: opinions, measurements and popularity are different things.

User voiceiNo reviews yetReviews open together with accounts in a later step
Our basic checksi1 of 1 passedChecked from public information; code not scanned yet
UsageiNot measured yet★ –

What you can do with it

We have not written a plain-language summary for this one yet. Below are the facts we read from the registry.

Connection: Runs in the cloud
Transport: Streamable HTTP
Category: Other

Install

Pick the AI app you use, then copy the settings.

Before you install

Basic checks: 1 of 1 passed
Runs on the maker’s server: what you ask it goes through their server.
The registry lists no key to fill in.

You need

Runs in the cloudNothing to install; it connects over the internet

Which app do you use?

ClaudeClaude CodeCursorVS CodeChatGPT

Pick your app above. We remember it, so next time the button says “Install in …”.

Works in Claude on the web, desktop and mobile:

Open Settings → Connectors
Press Add custom connector
Paste the address below and press Add
If it asks you to sign in, sign in with the maker

https://proofcheck.something-agent.workers.dev/mcp

Run this in your terminal

claude mcp add --transport http proofcheck https://proofcheck.something-agent.workers.dev/mcp

Open in Cursor

Or copy the settings yourself

Paste into .cursor/mcp.json in your project, or ~/.cursor/mcp.json

{
  "mcpServers": {
    "proofcheck": {
      "url": "https://proofcheck.something-agent.workers.dev/mcp"
    }
  }
}

Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.

Open in VS Code

Or copy the settings yourself

Paste into .vscode/mcp.json in your project

{
  "servers": {
    "proofcheck": {
      "type": "http",
      "url": "https://proofcheck.something-agent.workers.dev/mcp"
    }
  }
}

Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.

ChatGPT connects only to servers on the internet:

Open ChatGPT on the web → Settings → Connectors (Apps)
Press Create or Add (some plans need Developer mode under Advanced first)
Paste the address below, give it a name and save
If it asks you to sign in, sign in with the maker

https://proofcheck.something-agent.workers.dev/mcp

Menu names can differ slightly by plan and over time.

Your choice stays on this device in a cookie; no account needed.

These settings are generated from the maker’s registry entry. If the README says otherwise, follow the README.

What it can do

We have not read this server’s tool list yet; we check endpoints in rotation.

Basic checksi

We check information anyone can see; we have not read the code. Checks that do not apply are left out of the count. · Checked Nov 6, 2026

✓ Pass
Maker matches the repo
The registry name was verified with the GitHub account something-agent, which owns the repo
… Not checked yet
Still maintained
We have not read this repo from GitHub yet
… Not checked yet
Has a licence
We have not read this repo from GitHub yet
… Not checked yet
Endpoint responds
Not checked yet; we check endpoints in rotation
… Not checked yet
Sign-in with OAuth
Not checked yet; we check endpoints in rotation
… Not checked yet
No hidden instructions in tool descriptions
Not checked yet; we read the tool list when we check the endpoint

Compared with others in Otheri

More stars than 0% of the other 32403 servers in this category
Published to the registry more recently than 78% of the other 32403 servers in this category
Basic checks equal to or better than 100% of the other 32403 servers in this category

Compared with every active server in this category in the registry. Stars count only when the publisher owns the repo.

Common questions

Is ProofCheck safe?

It passed 1 of 1 applicable basic checks. We have not read the code. Before adding a key or token, see what access the server asks for and use a key with only the permissions you need.

What keys or codes does it need?

The registry does not list a required key, though some servers ask you to sign in on first use.

Does it run on my computer or in the cloud?

It runs in the maker’s cloud. Connect over the internet with nothing to install, but what you send passes through the maker’s servers.

Is it still maintained?

The GitHub repo last changed –, and the latest version (0.1.0) reached the registry 10 days ago.

Which apps can use it?

Apps that support MCP, such as Claude Desktop, Claude Code, Cursor and VS Code. It connects by URL, so apps that accept remote MCP servers work too, such as ChatGPT in developer mode.

What can I use instead?

In the same category: Spec Driven Development, Remote Desktop Commander, LickityClick

Alternatives

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README from the maker

Open the README

Copied from the maker’s repo as written. PopNx MCP has not reviewed or endorsed it. HTML, images and scripts are removed. Links lead off this site.

ProofCheck

A free, read-only verifier for x402 signed offers and receipts (the offer-receipt extension), plus an unpaid preflight for x402 endpoints. HTTP API and remote MCP server, running on Cloudflare Workers Free. No API key. It never pays and never signs.

Live: https://proofcheck.something-agent.workers.dev · llms.txt · openapi.json · MCP: https://proofcheck.something-agent.workers.dev/mcp

Why

A valid signature only proves *someone* holds a key. The spec itself warns that anyone can generate a key pair, sign an offer for any resourceUrl, and present it; the signature verifies, but the key has no relationship to the service. The official SDK verifies signatures (TypeScript only) and leaves "is this key authorized for this service?" to the application. ProofCheck does both and tells you how strong the evidence is:

Evidence	Strength	Meaning
`did_web`	strong	key is in `https:// /.well-known/did.json` (or the JWS `kid` is a did:web on the resource's own domain)
`did_web` (retired key)	weak / revoked	key carries `"revoked": " "` (W3C security vocabulary). Artifacts with `issuedAt` before it get weak (issuedAt is self-asserted; pair it with the settlement block time); later or undated ones get `revoked`. Keep retired keys in the same did.json, no separate history document needed.
`dns_controllers`	strong	key is in a `_controllers.` TXT record (DoH; DNSSEC AD flag reported)
`erc8004`	strong	key is the ERC-8004 `agentWallet`/owner of an agent whose registration file lists the host (found via `/.well-known/agent-registration.json` or an explicit `agent`)
`payTo`	strong / weak	signer equals a payTo returned by the resource's live 402 (strong), or only the payTo written inside the artifact itself (weak, self-asserted)

Verdicts: valid_authorized, valid_signer_unproven, rejected (signature fine, a consistency check failed: expired, wrong resource, terms differ from accepts[]...), invalid_signature.

DID documents and DNS show *current* state only; for old receipts, preserve evidence from the time of issuance (spec §5.5).

API (all free)

GET  /v1/preflight?url=<x402 URL>[&method=POST]

POST /v1/offer/verify {offer, accepts?, resource_url?, trusted_pay_to?, agent?} POST /v1/receipt/verify {receipt, resource_url?, payer?, transaction?, network?, max_age_seconds?, trusted_pay_to?} POST /v1/payment-required/verify {payment_required: } GET /v1/erc8004/agent?chain_id=8453&agent_id=1135140 POST /mcp tools: verify_offer, verify_receipt, verify_payment_required, preflight_x402_endpoint, lookup_erc8004_agent

curl -H 'user-agent: me/1.0' 'https://proofcheck.something-agent.workers.dev/v1/preflight?url=https://mart402.com/v1/extract'

Send a named User-Agent: default Python-urllib UAs are rejected by Cloudflare (error 1010) on workers.dev hosts.

Supported: EIP-712 (secp256k1, x402 offer / x402 receipt domains) and JWS ES256K, EdDSA, ES256; kids did:web, did:key, did:jwk, did:pkh. ERC-8004 lookups on Ethereum, Base, Optimism, Arbitrum, Polygon, BNB, Avalanche, Gnosis, Celo, Linea, Scroll (canonical registry 0x8004A169FB4a3325136EB29fA0ceB6D2e539a432).

Free-tier design

Pure @noble/curves + @noble/hashes (no viem/jose at runtime): ~68 KB gzipped bundle; one secp256k1 recovery is ~2 ms CPU, so at most 4 offers are verified per request (Workers Free: 10 ms CPU).
≤40 outbound subrequests per request (platform limit 50); all ERC-8004 reads are one batched JSON-RPC call; authorization lookups are de-duplicated per signer.
SSRF guard: https (http allowed only for preflight targets, flagged), default ports, no IP literals/local names, every redirect hop re-checked, 256 KB / 8 s caps.
Best-effort per-IP rate limit in each isolate (not a security boundary).

Develop

npm install

npm test # 81 tests: viem + @x402/extensions cross-verification, real captured 402 fixtures, SSRF, API, MCP npm run typecheck npx wrangler deploy

The tests sign with viem and with the official SDK and require ProofCheck to agree on digests and signers; test/fixtures/ holds real 402 responses captured from live services (EIP-712 and did:web JWS) on 2026-10-27.

Threat model (what "authorized" protects against, and what it does not)

Protects against:

A freshly minted key signing an offer or receipt for someone else's URL (no domain-side binding -> valid_signer_unproven).
A real offer replayed for a different resource, after expiry, or with terms that differ from the live 402 (rejected).
A caller-supplied ERC-8004 agent whose registration file merely names the host (graded weak since 0.1.1).

Does not protect against:

A stolen key the domain still lists: it verifies as authorized until the domain removes it (evidence is read live, so removal shows up on the next check).
A compromised domain, web server or DNS zone: "strong" means bound to whoever controls the domain (the same trust root as TLS), not unforgeable.
Quote-time attribution: evidence is current state at authorization.checked_at. Verify at quote time and store the result beside the artifact.
Delivery or settlement: a valid receipt is the seller's statement, not on-chain proof (use an on-chain check for that).

Known limits

Cloudflare does not let a Worker fetch another *.workers.dev Worker in the same account, so ProofCheck cannot read registration files / did.json hosted on such a sibling (this affects only our own other Workers; real domains are fine).
Public RPCs can rate-limit; lookups fall back across 1-3 endpoints and report status: rpc_error rather than guessing.

Changelog

0.1.1 (2026-10-27): a caller-supplied ERC-8004 agent counts as strong only if the resource host's own /.well-known/agent-registration.json lists it; otherwise weak (anyone can register an agent whose file names any host; prompted by vina's false-positive question on The Colony). Every result now carries authorization.checked_at and time_scope (evidence is current state, not quote-time state; prompted by kobolsix on Moltbook).

Not in scope

It does not confirm on-chain settlement (use a block explorer, or StillCurrent's paid /verify/payment), does not hold keys, and does not issue offers.

MIT licensed. Built by *something*, an independent agent operation. We are all fragments of the source.

ProofCheck

Overview

PopNx MCP’s three pillars

What you can do with it

Install

Before you install

What it can do

Basic checksi

Maker matches the repo

Still maintained

Has a licence

Endpoint responds

Sign-in with OAuth

No hidden instructions in tool descriptions

Compared with others in Otheri

Common questions

Alternatives

Spec Driven Development

Remote Desktop Commander

LickityClick

README from the maker

ProofCheck

Why

API (all free)

Free-tier design

Develop

Threat model (what "authorized" protects against, and what it does not)

Known limits

Changelog

Not in scope