The Tool Desk
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1. Pin the x402 version and validate the response shape
For a new v2 listing, confirm that the payment-required response uses x402Version: 2, includes the required resource object and accepts array, and follows the v2 field layout. Do not treat a v1 response as v2: the versions use different field names and placement. The x402 v2 specification defines the protocol shape; Cloudflare’s gateway guide, updated September 30, 2026, is an example of a vendor integration using v2.
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Because the specification and Bazaar guide are maintained on a moving repository branch, pin the released SDK or specification version—or a specific repository commit—in your implementation documentation. Recheck the version you deploy against the current source rather than mixing examples from v1 and v2.
2. Check that the resource and payment terms are the ones you intend to offer
Resource identity
Verify that resource.url identifies the public endpoint being protected. It should not point to staging, an internal hostname, or a different route. Check that the resource description and MIME type describe the paid result that the endpoint actually returns.
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Every payment option
For each entry in accepts, inspect the operational terms and compare them with both your intended offer and the payment implementation:
scheme: the payment scheme the route accepts.network: a CAIP-2 network identifier supported by the facilitator or local implementation.amount: the price in atomic units, not a human-readable display amount.asset: the asset used for payment.payTo: the intended recipient.maxTimeoutSeconds: the permitted payment timeout.
Check both syntax and meaning. A correctly formatted amount, for example, can still encode the wrong price. Confirm support for each scheme-and-network combination with the facilitator or local verifier you plan to use. The specification defines the payment-requirement format; Cloudflare’s documentation describes its own integration, not a universal provider requirement.
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3. Validate optional Bazaar discovery metadata
Bazaar service metadata is optional. If you include it, validate the documented limits before publishing; facilitators may silently discard invalid fields while retaining the rest of the metadata, as described in the Bazaar extension guide.
| Field | Documented limit or check |
|---|---|
serviceName |
At most 32 printable ASCII characters. |
tags |
At most five tags; each is at most 32 printable ASCII characters. |
iconUrl |
An absolute HTTP or HTTPS URL, at most 2,048 characters. The Bazaar guide restricts URLs to avoid IP literals and loopback hostnames. |
Do not assume that a listing has retained every submitted field just because the rest of it appears. Validate the metadata against the Bazaar guide, then inspect the resulting listing or discovery response where your workflow permits.
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4. Make the listing describe the API clients can actually call
Compare the advertised HTTP method, parameters, input schema, output example, and output schema with the behavior of the actual route. A schema that passes validation but describes a different route is misleading to clients. Give parameters useful descriptions so a caller can understand what to provide.
- Remove secrets, credentials, and personal identifiers from descriptions and example inputs or outputs.
- Use an output example that reflects the route’s real response rather than an idealized or unrelated payload.
- Check that the method and parameter names in the listing match the endpoint clients will call.
The Bazaar guide illustrates discovery metadata structures; that metadata does not establish that the API itself works.
Rank #4
- API Security in Action
- Manning Publications
- ABIS BOOK
5. Run a live preflight and payment test
- Call the protected endpoint without payment. Inspect the HTTP 402 response and its encoded
PAYMENT-REQUIREDdata. Confirm that it carries the version, resource, and payment options you reviewed. - Call it with the intended x402 client. Use the client and payment route you expect API users to use, with a facilitator or local verifier that supports the advertised scheme and network.
- Check the paid response and payment result. Confirm that the protected resource responds as intended and that verification and settlement complete successfully in that implementation.
There is an integration-specific detail for Cloudflare: its gateway design requires the origin to validate the signed PAYMENT-CONTEXT token before serving the request. That header is not a universal x402 requirement; follow the Cloudflare integration guide only when using that gateway design.
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Metadata checks establish whether the response and listing are well-formed and accurately describe the offer. They do not establish that a payment authorization is valid, that the recipient or amount is acceptable to your business, or that settlement will succeed.
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Under the default flow in the x402 v2 specification, the sequence is verify, resource, settle, response. Other flows may order checks differently, but the specification requires a verify or settle check before resource execution. Keep that security gate in the live request path: as the specification puts it, “The resource never executes with nothing checked.”
For a provider choice, compare the scheme and network combinations supported, its verification and settlement behavior, the operational requirements, and compatibility with your listing workflow. There is no basis here for ranking providers or claiming a particular validation success rate.
Quick Recap
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