Circle will open the Discovery API of Agent Marketplace on September 9th. Developers do not need the API key, authentication, or Circle account to query the x402 services provided by USDC through a public endpoint, and they can filter the results by category, network, price, and payment method. The returned results not only list the service addresses but also include information about the network, token contract, recipient wallet, atomic unit price, and input parameter structure, allowing agents to complete the closed-loop process of "discovery—pricing—payment—call" within their programs.
In the past, discussions about proxy payments mainly focused on wallets and signatures. However, a proxy first needs to know what services are available in the market, whether these services are online, and how their prices are structured. If each provider uses its own catalog and documentation, proxies still have to rely on manual configuration. Discovery API attempts to organize the payable interfaces into a machine-readable catalog that covers categories such as market data, web searches, media generation, predictive markets, and infrastructure.
What is returned is payment contract information, not an unlimited guarantee of service quality.
The official example endpoints are `https :// api.circle.com / v2 / x402 / discovery / resources`. Each record contains resource, type, accepts, and metadata. The accepts block uses CAIP-2 to identify the network, lists asset contracts, payTo addresses, and atomic unit amounts; metadata explains the provider, classification, interface description, inputs JSON Schema, as well as whether it supports regular x402 or Circle Gateway. USDC has six decimal places, and the value 8000 in the example represents 0.008 USDC.
Developers can filter by six categories and can also specify types such as network, http, or mcp, as well as the maximum price in US dollars and support for Gateway. The official reminds that to search for specific chains, one should use the structured network parameter instead of relying on free-text searches. This distinction is very practical: if a proxy mistakenly identifies " Base " in the description as a payment network, it might prepare funds for the wrong chain.
Circle ensures that the health and online status of directory services are monitored, and continuous sanctions screenings are conducted on sellers. This improves the quality of the directories, but it does not imply that Circle fully guarantees the content of the services, the accuracy of the output, or the legality of the business. Health checks can only prove that an endpoint is responsive at a given moment; they cannot verify the correctness of market data, ensure that generated content does not infringe on rights, or predict that the services are suitable for a particular jurisdiction. Users are still responsible for selecting trusted providers and defining the boundaries of their use.
There are two paths for payment: x402 using signed on-chain USDC transfers; Gateway Nanopayments adopting off-chain batch settlement to reduce the Gas friction of small payments. The icons in the directory indicate which path each service supports. The finality, refund methods, and dispute resolution processes for the two are different. Agents cannot simply choose based on the lowest price; they also need to consider network fees, settlement risks, response times, and compensation capabilities in case of failures.
For the proxy economy to scale, quota control and traceable procurement are more important than automatic payments.
The lack of key verification has lowered the threshold for detection and also expanded the potential targets for supply chain attacks. Malicious providers may use similar names, low prices, or enticing descriptions to attract agents. Production systems should fix the allowed categories, networks, and maximum unit prices, set trial quotas for new sellers, and verify whether the payment recipient addresses match those returned by the catalog. Catalog results should also be cached with timestamps, and prices should be re-confirmed before payment to avoid using outdated quotes.
Agents also need procurement strategies. The same search task may involve multiple services, and the lowest price does not necessarily yield the best results. The system can record success rates, delays, result consistency, and refund histories to gradually develop supplier ratings. For critical data, cross-verification from two independent services may even be conducted before deciding whether to use the results for transactions, risk control, or public release. It is found that API allows market searches, but the choice remains with the buyer.
Each micro-payment should leave behind information such as task ID, service resources, quotes, network details, assets, amount, payment recipient address, signer, and a return summary. Corporate finance needs to map a large number of small, online settlement records to specific business purposes; otherwise, amounts of less than one cent each can accumulate into unexplained accounts. It is best for agent wallets to have daily limits, task limits, and category limits, rather than having a balance that can be freely disposed of at will.
Directories also need to be exitable. Enterprises should retain the original service addresses and protocol specifications to avoid relying solely on a single directory for all their procurement processes; in the event that a directory becomes temporarily unavailable, they should be able to use verified caches or directly call upon existing suppliers. Caches must have set expiration dates, and the amount and address should be re-verified before payment is made. Transaction security should not be compromised for the sake of continuous operation.
This capability is already available through public endpoints, but the directory content and coverage will continue to change depending on service health, blockchain support, and compliance checks. What it addresses is how proxies can find and understand paid services; however, this does not mean that all listed services are suitable for direct purchase. A truly usable proxy market requires a combination of discovery, identity verification, payment, evaluation, refund options, and auditing. Circle has completed an important part of this process, but when enterprises integrate, they still need to strictly distinguish between what they "can afford" to pay and what they "should" pay.
