x402 Marketplaces and Paid APIs: Discovery to Delivery

Find a usable resource rather than a token listing

Here, marketplace means a place to discover payable services, such as a company-data API or document-conversion endpoint. It does not mean an exchange for a token with a similar name. Start with the result your agent needs and an interface it can call.

Suppose a research agent needs a structured company report. An illustrative seller charges $0.05 for one report and promises JSON containing the company identifier and source date. These are synthetic terms, not a live offer. They establish useful questions: which endpoint is called, what payment is accepted and how does the agent recognize a useful result?

Coinbase documents paid x402 resources, while the current Bazaar extension documentation describes a discovery layer with resource and payment metadata. Circle separately describes a machine-readable Agent Marketplace. These directories help discovery; their existence does not establish that every service suits your task or returns a valid result. [1] [2] [3]

Inspect the offer before signing

Keep the resource address, request method, required input and expected output together. A description saying company intelligence is too broad to show that an endpoint accepts your identifier or returns sources. Missing schema information is a reason to inspect the seller's documentation before paying.

Inspect the accepted scheme, network, asset, amount and recipient. Do not infer a human-readable amount without checking the asset denomination. Record relevant offer validity and payment timeout conditions. Your own HTTP request timeout is a different setting and should not be treated as proof that a payment expired.

The annotated card uses explanatory labels rather than an official protocol payload. An actual integration must parse the chosen version's schema and validate its required fields. A readable card helps a reviewer; the payment client needs the authoritative machine values underlying that display.

Separate discovery, payment and delivery

A search result establishes that a directory returned a resource. A current seller response establishes the offer at that time. A confirmed payment establishes a payment outcome. None of these alone proves that the report contains the requested information.

Keep a local purchase record connecting the resource, accepted offer, authorization decision and result. This is application design advice rather than an x402 field requirement. It gives the agent a way to investigate a timeout after payment without blindly starting a new paid attempt.

The response should match the requested company and expected format. A valid payment acknowledgement with an empty report is a delivery problem. A stale listing pointing to an unavailable endpoint is a discovery or availability problem. These findings require different next actions and should have different statuses in your records.

Compare discovery routes against your requirements

Evaluate a directory by how well it locates the resource and exposes its terms. Useful criteria include query support, payment filters, input/output metadata, timestamps and a documented invocation path. Listing counts alone do not establish quality, reach or successful purchases.

Bazaar documents structured discovery results and service search. Its discovery records can describe HTTP endpoints and MCP tools; invoking a selected resource still needs the appropriate client and payment route. Circle's marketplace belongs to Agent Stack. Keep these boundaries clear when deciding whether you need discovery, a wallet or a payment client. [2] [3]

X402 Hub is an affiliated product for x402 paid-resource discovery and payment integration. It provides another relevant starting point for an agent purchase workflow, and we disclose that relationship here. This page makes no claim about its listing count, market share, supported network breadth or measured purchase volume.

If you sell reports instead of buying them, begin with the seller integration guide. Make input, output, price and failure behavior understandable before pursuing directory inclusion. Discovery brings a buyer to an endpoint; the seller remains responsible for the promise made there.

Define a controlled first purchase

Choose one resource, one permitted payment route and an explicit purchase limit. Save the offer before signing. Define evidence of delivery and a place for a reviewer to inspect unresolved outcomes. A small payment still needs these records; its size does not make an unknown payment status disappear.

For the report, completion means receiving the correct report and linking it to the confirmed purchase. A changed offer requires policy evaluation again. An unknown payment outcome requires investigation before another paid attempt. Put those decisions alongside discovery, even when finding the resource is simple.

After the first integration, compare the discovery information with the actual seller response. If important terms differ, decide which source your application treats as authoritative and update the record. This is a useful operational check without pretending you have measured a directory's overall reliability from one example.