402Signal

Signed proof of what your agent was offered before it paid. 402Signal checks supported seller offers against buyer rules. On supported bound profiles, the local guard verifies signed evidence before your wallet signs; generic MPP offer observation does not itself provide a signed execution binding. Your application keeps its wallet, signing authority and final payment decision.

A qualifying check costs $0.003 USDC, paid over x402 with the same wallet. Completed normal misses are not settled: a check that finds no qualifying offer is free. Opening a hosted session costs $0.005 and lets you reuse one observation for 20 hops or 10 minutes. Seller payment, channel funding and network costs are separate, and a check is not a guarantee of delivery or output quality. Platform plans are quoted monthly on agreed receipt volume, workloads, capacity and support, with supported integration help and observation-triggered signed alerts. Start with a scoped evaluation. The quote states whether checking fees are included or separate. Private evidence stays in customer-owned storage; hosted retention is not included by default. See pricing.

Website · Try a sample check · Developer guides · Trust · OpenAPI · MCP · Changelog · Security policy

The service is also listed in third-party catalogues such as PayAPI Market (https://payapi.market/mcp); agents still pay https://402signal.com/route directly, and a listing is not an endorsement.

Three doors

Start in a minute

Official x402 client. One hook adds the check to your configured seller-payment path. It pays the fee with your own wallet, re-reads the seller's challenge, verifies the signed receipt with your pinned log key, and aborts a payment whose terms differ from what was verified:

npm install @402signal/[email protected] && npm audit signatures

import { signalGuard } from "@402signal/route-guard/x402";
client.onBeforePaymentCreation(signalGuard({ fetchWithPayment, trustedLogVkey }));

mppx. The same guard as an onChallenge hook: import { mppGuard } from "@402signal/route-guard/mpp".

Any language. Ask for the checking-fee terms without paying anything, then resend the identical request with the payment authorization:

curl -sS -D - https://402signal.com/route \
  -H 'Content-Type: application/json' \
  --data '{"need":"web search","networks":["base"],"max_price_usd":0.02,"require_route_binding":true}'

The HTTP 402 lists the fee requirements on Base, Solana and Algorand. Use url for an exact endpoint or need to discover candidates; networks is a hard filter and prefer_network only ranks. Over MCP, call the check tool with the same arguments (route, its former name, is still accepted).

Python. pip install 402signal gives you the unpaid challenge, the paid check, read-only recovery and an offline receipt verifier (signal402.verify.verify_route_receipt).

No wallet yet? Run a sample check in the browser against a listed endpoint, ask for free check credits at [email protected] (listed endpoints only), or run the offline checks with Node.js 22 or newer:

node integration/buyer-checks/run.mjs

The client and guard are published on npm with a provenance attestation and as GitHub release archives with checksums; from a reviewed checkout node scripts/install_route_guard.mjs downloads, verifies and installs the current release.

What a check returns

Read live, payable, selected_payment and billing together. A settled fee is not reversed if the seller's offer later changes.

Keys, credits and alerts

• Check credits (X-402Signal-Trial): operator-issued, listed endpoints only, for evaluation without a funded wallet.
• Admission keys (X-402Signal-Key): agreed ingress and capacity for platforms; never a wallet key.
• GET /keys/usage answers only for the credentials you present: remaining credits, ceiling, expiry, or the key's recognized capacity.
• Change alerts: with a key, POST /alerts subscribes a public HTTPS webhook to up to 20 seller hosts and delivers signed price_changed, recipient_changed and liveness_changed events drawn from the same public observations the endpoint pages count. Guide: docs/customer/alerts.md.

Evidence

Every qualifying check with require_route_binding returns an Ed25519-signed receipt bound to the exact URL, method, body hash and the seller's current x402 envelope, with an inclusion proof in an append-only log whose checkpoints are anchored on Algorand MainNet with a Falcon-1024 signature. Clients that need later verification must securely retain the complete paid /route response, including pq_trust.transparency.receipt and pq_trust.transparency.reveal, together with the original request. Private replay outcomes are short-term recovery, not long-term evidence storage. The reveal contains private request and decision evidence; do not put it in public logs.

The record format is documented as the Offer Evidence Record, version 1, with a draft x402 extension proposal. Verify a saved record with verifyReceipt from the guard, with the Python package, or in the browser at 402signal.com/verify; inspect the public log at 402signal.com/transparency.

What is in this repository

Develop

Python 3.12.14 and Node 24, matching CI. Fixture mode keeps every catalog and seller response synthetic; no test needs a wallet, a facilitator or the network.

python3 -m pip install --require-hashes -r requirements.txt
LIVE402_FIXTURE=1 PYTHONPATH=. python3 -m live402          # http://127.0.0.1:8081
LIVE402_FIXTURE=1 PYTHONPATH=. python3 -m unittest discover -s tests
npm --prefix sdk/route-guard test

LOCAL_FREE=1 skips the paywall for local development and must never be set in production. See CONTRIBUTING.md for branches, reviews and the release train, and the documentation index for the replay authority, readiness, backups and scaling plans. Historical TestNet broadcasting is a 402signal (router) env capability: a security review must approve before anyone sets it to 1. Signer never reads BROADCAST, and the flag does not enable MainNet anchoring, which has its own reviewed runbook.

Contact

MIT license · Security reports · [email protected] · @402Signal