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# Agent stack
Source: https://developers.circle.com/agent-stack
Empower your AI agents to autonomously operate wallets, transact onchain, and pay for API services through Circle's agent-native tooling.
Circle Agent Stack lets your AI agent hold and transact USDC and other tokens
across blockchains, discover and pay for x402 services, and operate within
built-in compliance guardrails. Use with
[Claude Code](https://claude.com/claude-code), [Cursor](https://cursor.com/),
[Codex](https://openai.com/codex), [OpenClaw](https://openclaw.ai/), or any
custom AI agent.
## What you can do
* **Build with an agent-native interface**: Use
[Circle CLI](/agent-stack/circle-cli) and [Circle Skills](/ai/skills) to give
your agent access to [Circle Wallets](/wallets), [CCTP](/cctp), and
[Gateway](/gateway) from a single command interface.
* **Give your AI agent wallets**: Use
[Agent wallets](/agent-stack/agent-wallets) to hold and spend USDC and other
tokens with customizable spending controls and built-in compliance guardrails.
* **Discover and pay for services on demand**: Search
[x402-compatible APIs](https://agents.circle.com/services) and pay per
request, without subscriptions or API keys.
* **Operate onchain across blockchains**: Trade tokens, bridge USDC, and execute
onchain strategies across
[supported blockchains](/agent-stack/agent-wallets/supported-blockchains).
## The agent stack
<CardGroup>
<Card title="Circle CLI" icon="terminal" href="/agent-stack/circle-cli">
A command-line tool for managing agent wallets, installing skills, and
accessing the Circle product suite from any agent framework.
</Card>
<Card title="Agent Wallets" icon="wallet" href="/agent-stack/agent-wallets">
Wallets for AI agents with custom spending policies, multichain support, and
built-in compliance controls. Gasless across blockchains.
</Card>
<Card title="Agent Nanopayments" icon="bolt" href="/agent-stack/agent-nanopayments">
Gasless USDC payments at sub-cent scale. Pay for x402-compatible services
from your AI agent. Powered by Gateway.
</Card>
<Card title="Agent Marketplace" icon="store" href="/agent-stack/agent-marketplace">
A curated, compliance-first service catalog where AI agents can discover and
pay for USDC-priced services.
</Card>
<Card title="Facilitator Service" icon="bolt" href="/facilitator-service">
Circle's hosted x402 facilitator for sellers. Accept x402 payments in USDC
on Arc, Base, and Polygon PoS without operating a relayer.
</Card>
<Card title="Gateway Nanopayments" icon="layer-group" href="/gateway-nanopayments">
Gas-free USDC nanopayments down to \$0.000001, batched by Circle Gateway. Pay
for x402 resources without gas on every call.
</Card>
<Card title="Circle Skills" icon="puzzle-piece" href="/ai/skills">
Open-source skills that give your AI agent specialized knowledge for
building with Circle products.
</Card>
</CardGroup>
## Dive deeper
* Get started with the
[Agent Wallets quickstart](/agent-stack/agent-wallets/quickstart).
* Make your first nanopayment with the
[Agent Nanopayments quickstart](/agent-stack/agent-nanopayments/quickstart).
* Accept x402 payments as a seller with the
[Facilitator Service quickstart](/facilitator-service/quickstart).
* Send gas-free USDC nanopayments with the
[Gateway Nanopayments buyer quickstart](/gateway-nanopayments/quickstarts/buyer).
* Browse [Circle CLI commands](/agent-stack/circle-cli/command-reference).
# Agent marketplace
Source: https://developers.circle.com/agent-stack/agent-marketplace
A curated, compliance-first catalog of x402 services that accept USDC, built for AI agents to discover and pay per request.
The Agent Marketplace is a curated catalog of
[x402](/x402-facilitators/x402)-compatible services that accept USDC. Every
listing is screened (each seller's payout wallet is continuously
sanctions-checked) and continuously health-checked, so your agent finds services
that are compliant and live.
Buyers and sellers meet here. Buyers (AI agents) find services and pay per
request, with no subscriptions, no accounts, and no API keys. Sellers (API
owners) list a service once and get paid in USDC for each call.
Browse the catalog at
[agents.circle.com/services](https://agents.circle.com/services), or query it
programmatically with the
[Discovery API](/agent-stack/agent-marketplace/discovery-api).
## Explore
<CardGroup>
<Card title="Discovery API" icon="magnifying-glass" href="/agent-stack/agent-marketplace/discovery-api">
Query the public catalog over one HTTP endpoint. Filter by network, price,
payment rail, and protocol type. No API key.
</Card>
<Card title="Become a seller" icon="money-bill" href="/agent-stack/agent-marketplace/become-a-seller">
Monetize your API by charging agents per request in USDC. Scaffold it in
minutes with a Circle Skill.
</Card>
<Card title="Get listed" icon="list-check" href="/agent-stack/agent-marketplace/get-listed">
Submit your service for review. Once approved, it appears in the catalog and
the Discovery API.
</Card>
<Card title="Browse the catalog" icon="store" href="https://agents.circle.com/services">
Explore 600+ live services across 15+ blockchain networks in your browser.
</Card>
</CardGroup>
## How a paid request works
Every service in the catalog follows the same [x402](/x402-facilitators/x402)
handshake:
1. An agent calls the service with no payment. The service responds
`402 Payment Required`, plus a machine-readable price list (the `accepts`
array). Each entry states which token (`asset`), on which blockchain
(`network`), how much (`amount`), and to which address (`payTo`).
2. The agent's wallet picks an option it can pay, signs a USDC payment, and
retries the request with the signed payment attached.
3. The service settles the payment and returns the real response.
No accounts, no API keys: the payment is the authentication.
## Why the Agent Marketplace
* **One integration, many blockchains**: A single query returns services priced
across 15+ networks. No per-chain registry hunting.
* **Curated, not scraped**: Filter 600+ services by query, network, price,
payment rail, and protocol type, instead of parsing thousands of raw
endpoints.
* **Compliance built in**: Each seller's payout wallet is continuously
sanctions-screened. Blocked sellers drop out, so you inherit a watchlist-clean
catalog.
* **Agent-native responses**: Each listing ships structured payment requirements
plus input and output JSON Schema, so any wallet can construct and execute
payment without a human reading docs.
* **Live, not stale**: Endpoints are continuously health-checked, and
unreachable ones are auto-excluded.
* **Standards-based**: CAIP-2 networks, the x402 protocol, the
[x402 Bazaar](https://docs.x402.org/extensions/bazaar) discovery schema, and
OpenAPI and A2A discovery surfaces. No API key, no account.
# How-to: Become a seller
Source: https://developers.circle.com/agent-stack/agent-marketplace/become-a-seller
Monetize your API by charging AI agents per request in USDC, with no API keys and no invoices.
Make your API charge AI agents per request in USDC over
[x402](/x402-facilitators/x402): your endpoint returns `402 Payment Required`
when a request is unpaid, and serves the resource when a valid payment is
attached. There are no API keys to issue, no invoices to send, and no accounts
to manage. Follow these steps to take an Express API from zero to paid and ready
to [list in the Agent Marketplace](/agent-stack/agent-marketplace/get-listed).
<Tip>
The `accept-agent-payments` [Circle Skill](/ai/skills) scaffolds these steps
directly in your codebase. Install it in your AI IDE with `circle skill
install --tool claude-code --name accept-agent-payments` (or see the other
install options on the [skills page](/ai/skills)), then ask your agent to add
agent payments to your service.
</Tip>
## Prerequisites
Before you begin, ensure that you've:
* Obtained an EVM wallet address to receive USDC. Buyers pay to this address,
and only you control it. If you don't have one, create an
[agent wallet](/agent-stack/agent-wallets/quickstart) with Circle CLI.
* Built an HTTP API that you can add payment middleware to.
* Installed [Node.js](https://nodejs.org/) v22.18+.
* Chosen a price per request (for example, `$0.01`; sub-cent prices work too).
## Steps
### Step 1. Install the SDK
```shell theme={null}
npm install @circle-fin/x402-batching @x402/core @x402/evm viem express
```
### Step 2. Return 402 and settle payments
Add the Gateway middleware and put a price on a route. Set `sellerAddress` to
your payout wallet address; buyers see it as the `payTo` address in the price
list your endpoint returns:
```ts server.ts theme={null}
import express from "express";
import { createGatewayMiddleware } from "@circle-fin/x402-batching/server";
const app = express();
const gateway = createGatewayMiddleware({
sellerAddress: "0xYOUR_WALLET_ADDRESS", // your payout wallet
facilitatorUrl: "https://gateway-api-testnet.circle.com", // testnet
});
app.get("/premium-data", gateway.require("$0.01"), (req, res) => {
res.json({ data: "Your paid content" });
});
app.listen(3000);
```
`gateway.require("$0.01")` returns `402 Payment Required` with the payment
options for unpaid requests, and settles valid payments with Gateway before your
handler runs. Full walkthrough:
[Gateway Nanopayments seller quickstart](/gateway-nanopayments/quickstarts/seller).
### Step 3. Accept vanilla x402 too
The preceding middleware accepts
[Gateway nanopayments](/agent-stack/agent-nanopayments): gasless, sub-cent
payments settled offchain in batches. To also accept onchain x402 payments and
reach buyers on non-Circle x402 stacks, run an `x402ResourceServer` with an x402
facilitator alongside the Gateway scheme:
```ts theme={null}
import { x402ResourceServer } from "@x402/express";
import { HTTPFacilitatorClient } from "@x402/core/server";
import {
BatchFacilitatorClient,
GatewayEvmScheme,
} from "@circle-fin/x402-batching/server";
const server = new x402ResourceServer([
new HTTPFacilitatorClient({ url: "https://facilitator.example.com" }),
new BatchFacilitatorClient(),
]);
server.register("eip155:*", new GatewayEvmScheme());
await server.initialize();
```
`GatewayEvmScheme` extends the standard onchain scheme, so your `402` responses
offer both rails in one `accepts` array and buyers pick whichever they have
funded. Details:
[Add nanopayments to an x402 seller](/gateway-nanopayments/howtos/x402-seller).
<Tip>
Supporting both rails maximizes the buyers who can transact with you, the same
way a merchant accepts more than one card network. For the same reason, accept
payment on more than one blockchain (for example, Base and Polygon PoS): a
buyer can only pay from a blockchain where you accept it.
</Tip>
### Step 4. Test the handshake
Send an unpaid request and confirm the `402`:
```shell theme={null}
curl -i http://localhost:3000/premium-data
```
You should see `402 Payment Required` with a `PAYMENT-REQUIRED` header that
carries the payment options. Then pay it end to end with the
[buyer quickstart](/gateway-nanopayments/quickstarts/buyer) client or the Circle
CLI
[pay for a service](/agent-stack/agent-nanopayments/operations/pay-for-service)
flow.
### Step 5. Check earnings and withdraw
Gateway payments accumulate in your Gateway balance and batch-settle onchain.
Check and withdraw with `GatewayClient`:
```ts theme={null}
import { GatewayClient } from "@circle-fin/x402-batching/client";
const client = new GatewayClient({
chain: "arcTestnet",
privateKey: process.env.PRIVATE_KEY as `0x${string}`,
});
const balances = await client.getBalances();
console.log(`Available: ${balances.gateway.formattedAvailable} USDC`);
await client.withdraw("50");
```
## See also
* [How-to: Get listed](/agent-stack/agent-marketplace/get-listed): put your live
endpoint in the marketplace catalog.
* [Seller integration tools](/agent-stack/agent-nanopayments/seller-integration-tools):
third-party platforms that run the payment layer for you if you are not on
Express.
* [What is x402?](/x402-facilitators/x402): the payment handshake behind these
steps.
# Discover x402 services
Source: https://developers.circle.com/agent-stack/agent-marketplace/discovery-api
openapi/agent-marketplace-discovery.yaml get /v2/x402/discovery/resources
One public endpoint to discover x402 services that accept USDC, across many blockchains. No API key, no account.
## Categories
Every listing is classified with one category in `metadata.provider.category`.
Filter on it with the `category` query parameter to narrow results to a domain.
| Category | Description |
| :- | :- |
| `SOCIAL_INTELLIGENCE` | Social platform data and audience or sentiment signals. |
| `FINANCIAL_ANALYSIS` | Market data, prices, and financial analytics. |
| `WEB_SEARCH_RESEARCH` | Web search, scraping, and research retrieval. |
| `PREDICTION_MARKETS` | Odds, forecasts, and prediction-market data. |
| `CREATIVE` | Media generation such as images, audio, and text. |
| `INFRASTRUCTURE` | Developer tooling and infrastructure utilities. |
## Paying for a service
Discovery tells you what each service accepts. To actually pay, use one of two
rails:
* **Vanilla x402**: a signed onchain USDC transfer that any USDC wallet,
including a centralized custodial one, can produce.
* **Circle Gateway**: offchain, batched settlement for gasless, sub-cent
payments.
Each listing's `accepts[]` and its `supportsVanillax402` and
`supportsCircleGateway` flags tell you which rails it takes. To pay from Circle
CLI, see
[Pay for a service](/agent-stack/agent-nanopayments/operations/pay-for-service).
For the concepts and buyer integration, see
[Agent nanopayments](/agent-stack/agent-nanopayments).
<Tip>
To find services payable on a specific blockchain, filter with the structured
`network` parameter, not the `query` text field. `query` matches free text
(URLs, providers, descriptions, tags), so it does not reliably match a chain.
</Tip>
## Related
* [Service catalog](https://agents.circle.com/services)
* [OpenAPI spec](https://agents.circle.com/.well-known/openapi.json)
* [A2A card](https://agents.circle.com/.well-known/a2a.json)
* [Agent skills index (llms.txt)](https://agents.circle.com/llms.txt)
# How-to: Get listed
Source: https://developers.circle.com/agent-stack/agent-marketplace/get-listed
Submit your x402 service for review to appear in the Agent Marketplace catalog and the Discovery API.
List your service in the [Agent Marketplace](/agent-stack/agent-marketplace) so
agents can discover and pay for it. Approved listings appear in both the
[catalog UI](https://agents.circle.com/services) and the
[Discovery API](/agent-stack/agent-marketplace/discovery-api), where agents
filter by category, network, and price.
<Info>
Listings are reviewed and approved manually today. A self-serve, automated
submission flow is coming. For now, submit the form below and the team reviews
your service.
</Info>
## Prerequisites
Before you begin, ensure that you've:
* Made your service payable: it returns `402 Payment Required` when a request is
unpaid and serves the resource when paid. See
[How-to: Become a seller](/agent-stack/agent-marketplace/become-a-seller).
* Published an OpenAPI spec for your service, so agents can read its inputs and
outputs.
* Confirmed the payout wallet address your service uses. You submit it with the
form, and it is sanctions-screened during review.
## Steps
<Steps>
<Step title="Submit the intake form">
Submit your service details at the [intake
form](https://forms.gle/7YFzvdmMcn1JH5tF6). Include your endpoint URL,
payout wallet address, and a short description.
</Step>
<Step title="Review">
The team screens and approves your submission. Your seller payout wallet is
sanctions-screened as part of review.
</Step>
<Step title="Go live">
Once approved, your service appears in the catalog and is returned by the
Discovery API. It is then continuously health-checked, so it stays listed
only while it is reachable. Agents find you through the [Discovery
API](/agent-stack/agent-marketplace/discovery-api) filters, so make sure
your metadata makes your service easy to find.
</Step>
</Steps>
# Agent Nanopayments
Source: https://developers.circle.com/agent-stack/agent-nanopayments
Gas-free, batched USDC payments at sub-cent scale for AI agents.
Agent Nanopayments, built on [Gateway Nanopayments](/gateway-nanopayments), let
your AI agent pay for [x402](/x402-facilitators/x402)-compatible services in
sub-cent USDC. These payments would normally be uneconomical due to per-payment
gas costs, but batching them into a single onchain settlement makes
high-frequency machine-to-machine commerce viable.
Your agent uses [Circle CLI](/agent-stack/circle-cli) to deposit USDC into a
Gateway balance, discover services, and pay for them.
## Get started
Follow the [quickstart](/agent-stack/agent-nanopayments/quickstart) to deposit
USDC, find a service, and make a nanopayment.
## Use cases
<CardGroup>
<Card title="Pay for APIs and services" icon="bolt">
Pay for x402-compatible APIs on a per-request basis. No subscriptions or
per-service sign-ups.
</Card>
<Card title="On-demand compute and data" icon="server">
Pay for compute, data, or storage at usage scale. Sub-cent payments make
granular billing viable.
</Card>
<Card title="Agent-to-agent commerce" icon="arrows-left-right">
Enable machine-to-machine payments at high frequency, with batched
settlement keeping costs predictable.
</Card>
<Card title="Service discovery" icon="store">
Find x402-compatible services on [Circle Agent
Marketplace](https://agents.circle.com/services) and pay using your [agent
wallet](/agent-stack/agent-wallets).
</Card>
</CardGroup>
## Features
<AccordionGroup>
<Accordion title="Batched settlement" icon="gas-pump">
Gateway batches many payment authorizations and settles them onchain in a
single transaction, amortizing gas across thousands of payments. Your agent
pays no per-transaction gas. Learn more about [batched
settlement](/gateway-nanopayments/concepts/batched-settlement).
</Accordion>
<Accordion title="x402 protocol" icon="code">
Nanopayments use the [x402 standard](/x402-facilitators/x402), an open
HTTP-native payment protocol built around the `402 Payment Required` status
code. Sellers declare payment requirements, your agent signs a payment
payload, and the exchange happens in a single request-response cycle.
</Accordion>
<Accordion title="Crosschain balance" icon="arrow-right-arrow-left">
Your nanopayments balance can live on any [Gateway-supported
blockchain](/gateway/references/supported-blockchains).
</Accordion>
</AccordionGroup>
<Tip>
To integrate x402 and Gateway Nanopayments in your application code instead of
Circle CLI, see the [Gateway Nanopayments buyer
quickstart](/gateway-nanopayments/quickstarts/buyer).
</Tip>
# Nanopayment operations
Source: https://developers.circle.com/agent-stack/agent-nanopayments/operations
Tasks your agent can perform using Circle CLI to deposit USDC, pay for services, and withdraw funds.
Nanopayment operations are tasks your agent can perform using
[Circle CLI](/agent-stack/circle-cli). Full command syntax is in the
[CLI command reference](/agent-stack/circle-cli/command-reference).
The following table describes common nanopayment operations and the CLI commands
to perform them.
| Operation | What it does | Command |
| :- | :- | :- |
| [Deposit for nanopayments](/agent-stack/agent-nanopayments/operations/deposit) | Add USDC to your Gateway balance to fund nanopayments. | `circle gateway deposit` |
| [Pay for a service](/agent-stack/agent-nanopayments/operations/pay-for-service) | Discover and pay for [x402](/x402-facilitators/x402)-compatible API services using USDC. | `circle services pay` |
| [Withdraw your balance](/agent-stack/agent-nanopayments/operatio프로젝트로 돌아가기
