{ "type": "stack", "id": "agent-that-can-buy-things", "title": "Agent that can buy things", "summary": "The pieces for an agent that pays for APIs per call with x402 stablecoins and buys from merchants with controlled virtual cards, with spend limits, proof of user intent and a full audit trail.", "author": "Agentica Author", "tags": [ "payments", "agent-commerce", "x402", "stablecoins", "cards", "guardrails" ], "published": "2026-10-02", "last_verified": "2026-10-02", "entries": [ "claude-agent-sdk", "x402", "coinbase-agentic-wallet", "usdc", "x402-bazaar", "cdp-x402", "stripe-issuing-for-agents", "agentic-commerce-protocol", "universal-commerce-protocol", "agent-payments-protocol", "stripe-agentic-commerce", "machine-payments-protocol", "browserbase", "langfuse" ], "links": { "html": "https://indexagentica.com/stacks/agent-that-can-buy-things/", "markdown": "https://indexagentica.com/stacks/agent-that-can-buy-things.md", "json": "https://indexagentica.com/api/longform/stacks/agent-that-can-buy-things.json", "source": "https://github.com/Drudley/indexagentica/blob/main/content-long/stacks/agent-that-can-buy-things.md" }, "status": "published", "stack": { "use_case": "Let an agent pay for metered APIs and tools on its own and complete merchant purchases for a user, within budgets you set and with a record of who authorized what.", "components": [ { "role": "Agent harness", "entry": "claude-agent-sdk", "name": "Claude Agent SDK", "url": "https://indexagentica.com/entries/claude-agent-sdk/", "why": "Runs the agent loop with tools, skills and MCP in your own app, so payment tools sit behind code you control rather than prompts. Any harness with tool calling works." }, { "role": "Machine payment protocol", "entry": "x402", "name": "x402", "url": "https://indexagentica.com/entries/x402/", "why": "Pay per request for HTTP APIs and MCP tools: the server answers 402 with a price, the agent signs a stablecoin payment and retries. SDKs default to USD stablecoins and a $1 cap per payment." }, { "role": "Agent wallet", "entry": "coinbase-agentic-wallet", "name": "Coinbase Agentic Wallet", "url": "https://indexagentica.com/entries/coinbase-agentic-wallet/", "why": "A wallet built for agents, as the awal CLI with skills or as an MCP server (npx @coinbase/payments-mcp), that pays x402 services with guardrails such as a per-call maximum amount." }, { "role": "Settlement currency", "entry": "usdc", "name": "USDC", "url": "https://indexagentica.com/entries/usdc/", "why": "The stablecoin most x402 services price in. Fund the agent's wallet with only what it may spend, and test on Base Sepolia with faucet USDC first." }, { "role": "Service discovery", "entry": "x402-bazaar", "name": "x402 Bazaar", "url": "https://indexagentica.com/entries/x402-bazaar/", "why": "A public index of x402-payable endpoints with prices and schemas, so the agent can find a paid API without a human signing up for keys." }, { "role": "Card credentials", "entry": "stripe-issuing-for-agents", "name": "Stripe Issuing for Agents", "url": "https://indexagentica.com/entries/stripe-issuing-for-agents/", "why": "Single-use or per-agent virtual cards with spend limits, merchant-category controls and real-time authorization webhooks, usable for programmatic checkout (MPP, UCP, Shared Payment Tokens) or in a browser." }, { "role": "Merchant checkout protocol", "entry": "agentic-commerce-protocol", "name": "Agentic Commerce Protocol (ACP)", "url": "https://indexagentica.com/entries/agentic-commerce-protocol/", "why": "OpenAI and Stripe's open checkout standard (beta); lets an agent complete a purchase through a merchant's agent-ready checkout with a delegated payment token." }, { "role": "Merchant checkout protocol (alternative)", "entry": "universal-commerce-protocol", "name": "Universal Commerce Protocol (UCP)", "url": "https://indexagentica.com/entries/universal-commerce-protocol/", "why": "Capability-based commerce standard over REST, MCP or A2A, covering checkout, identity linking and orders, with support for AP2 mandates." }, { "role": "Proof of user intent", "entry": "agent-payments-protocol", "name": "Agent Payments Protocol (AP2)", "url": "https://indexagentica.com/entries/agent-payments-protocol/", "why": "Signed Checkout and Payment Mandates record what the user authorized, either a specific purchase or constraints like a budget, giving merchants and you an audit trail." }, { "role": "Browser for non-agent checkouts", "entry": "browserbase", "name": "Browserbase", "url": "https://indexagentica.com/entries/browserbase/", "why": "A hosted browser for merchants without an agent-checkout API, kept apart from your own machine and sessions." }, { "role": "Tracing", "entry": "langfuse", "name": "Langfuse", "url": "https://indexagentica.com/entries/langfuse/", "why": "Records every tool call and payment decision so you can reconcile spend against what the agent did and why." } ] }, "entries_detail": [ { "id": "claude-agent-sdk", "name": "Claude Agent SDK", "summary": "Anthropic's SDK for building production agents with Claude Code as a library, in Python and TypeScript.", "url": "https://indexagentica.com/entries/claude-agent-sdk/", "json": "https://indexagentica.com/api/entries/claude-agent-sdk.json" }, { "id": "x402", "name": "x402", "summary": "Open standard for internet-native payments built on HTTP 402, letting APIs and agents pay per request across crypto and fiat networks.", "url": "https://indexagentica.com/entries/x402/", "json": "https://indexagentica.com/api/entries/x402.json" }, { "id": "coinbase-agentic-wallet", "name": "Coinbase Agentic Wallet", "summary": "Wallet tooling that lets AI agents hold, spend, trade and earn stablecoins with guardrails, via the awal CLI + skills or an MCP server.", "url": "https://indexagentica.com/entries/coinbase-agentic-wallet/", "json": "https://indexagentica.com/api/entries/coinbase-agentic-wallet.json" }, { "id": "usdc", "name": "USDC", "summary": "Fully reserved dollar stablecoin issued by Circle, the settlement asset used by many agent payment rails including x402.", "url": "https://indexagentica.com/entries/usdc/", "json": "https://indexagentica.com/api/entries/usdc.json" }, { "id": "x402-bazaar", "name": "x402 Bazaar", "summary": "Public catalog of x402 payment-gated services discovered by the CDP Facilitator; search by intent, browse resources or look up by merchant address.", "url": "https://indexagentica.com/entries/x402-bazaar/", "json": "https://indexagentica.com/api/entries/x402-bazaar.json" }, { "id": "cdp-x402", "name": "Coinbase CDP x402 Facilitator", "summary": "Coinbase Developer Platform's x402 offering: a hosted facilitator that verifies and settles x402 payments, plus seller and buyer SDK quickstarts.", "url": "https://indexagentica.com/entries/cdp-x402/", "json": "https://indexagentica.com/api/entries/cdp-x402.json" }, { "id": "stripe-issuing-for-agents", "name": "Stripe Issuing for Agents", "summary": "Issue cards and credentials that agents can use to purchase autonomously, with spend controls, real-time authorization decisioning and full visibility.", "url": "https://indexagentica.com/entries/stripe-issuing-for-agents/", "json": "https://indexagentica.com/api/entries/stripe-issuing-for-agents.json" }, { "id": "agentic-commerce-protocol", "name": "Agentic Commerce Protocol (ACP)", "summary": "Open standard from OpenAI and Stripe for programmatic checkout flows between buyers, their AI agents and businesses.", "url": "https://indexagentica.com/entries/agentic-commerce-protocol/", "json": "https://indexagentica.com/api/entries/agentic-commerce-protocol.json" }, { "id": "universal-commerce-protocol", "name": "Universal Commerce Protocol (UCP)", "summary": "Open standard giving platforms (AI agents, apps), businesses, payment service providers and credential providers a common language for commerce.", "url": "https://indexagentica.com/entries/universal-commerce-protocol/", "json": "https://indexagentica.com/api/entries/universal-commerce-protocol.json" }, { "id": "agent-payments-protocol", "name": "Agent Payments Protocol (AP2)", "summary": "Open protocol for AI agents to make payments on behalf of users securely, complementing A2A and MCP.", "url": "https://indexagentica.com/entries/agent-payments-protocol/", "json": "https://indexagentica.com/api/entries/agent-payments-protocol.json" }, { "id": "stripe-agentic-commerce", "name": "Stripe Agentic Commerce", "summary": "Stripe integrations for selling through agents and embedding commerce in AI interfaces, including Shared Payment Tokens for agent-initiated purchases.", "url": "https://indexagentica.com/entries/stripe-agentic-commerce/", "json": "https://indexagentica.com/api/entries/stripe-agentic-commerce.json" }, { "id": "machine-payments-protocol", "name": "Machine Payments Protocol (MPP)", "summary": "Open standard for machine-to-machine payments over HTTP 402, co-developed by Tempo and Stripe; charge per API request, tool call or content.", "url": "https://indexagentica.com/entries/machine-payments-protocol/", "json": "https://indexagentica.com/api/entries/machine-payments-protocol.json" }, { "id": "browserbase", "name": "Browserbase", "summary": "Hosted headless-browser infrastructure that gives agents access to the whole web.", "url": "https://indexagentica.com/entries/browserbase/", "json": "https://indexagentica.com/api/entries/browserbase.json" }, { "id": "langfuse", "name": "Langfuse", "summary": "Open-source agent evals and observability platform: trace, evaluate and improve LLM applications and agents.", "url": "https://indexagentica.com/entries/langfuse/", "json": "https://indexagentica.com/api/entries/langfuse.json" } ], "related": [ { "type": "guide", "id": "pay-for-an-api-with-x402", "title": "Pay for an API as an agent with x402", "url": "https://indexagentica.com/guides/pay-for-an-api-with-x402/", "json": "https://indexagentica.com/api/longform/guides/pay-for-an-api-with-x402.json" }, { "type": "skill", "id": "pay-with-x402", "title": "Pay with x402", "url": "https://indexagentica.com/skills/pay-with-x402/", "json": "https://indexagentica.com/api/longform/skills/pay-with-x402.json" }, { "type": "comparison", "id": "agent-payment-rails", "title": "Agent payment protocols compared", "url": "https://indexagentica.com/compare/agent-payment-rails/", "json": "https://indexagentica.com/api/longform/compare/agent-payment-rails.json" }, { "type": "guide", "id": "run-untrusted-code-in-a-sandbox", "title": "Run agent-generated code safely in a sandbox", "url": "https://indexagentica.com/guides/run-untrusted-code-in-a-sandbox/", "json": "https://indexagentica.com/api/longform/guides/run-untrusted-code-in-a-sandbox.json" } ], "sources": [ { "title": "x402 Protocol Specification v2", "url": "https://github.com/x402-foundation/x402/blob/main/specs/x402-specification-v2.md", "accessed": "2026-10-02" }, { "title": "x402 docs, Quickstart for Buyers", "url": "https://docs.x402.org/getting-started/quickstart-for-buyers", "accessed": "2026-10-02" }, { "title": "Coinbase CDP, Agentic Wallet overview", "url": "https://docs.cdp.coinbase.com/agentic-wallet/welcome", "accessed": "2026-10-02" }, { "title": "x402 docs, Bazaar (Discovery Layer)", "url": "https://docs.x402.org/extensions/bazaar", "accessed": "2026-10-02" }, { "title": "Stripe docs, Issuing for agents", "url": "https://docs.stripe.com/issuing/agents", "accessed": "2026-10-02" }, { "title": "Agentic Commerce Protocol repository", "url": "https://github.com/agentic-commerce-protocol/agentic-commerce-protocol", "accessed": "2026-10-02" }, { "title": "Universal Commerce Protocol repository", "url": "https://github.com/Universal-Commerce-Protocol/ucp", "accessed": "2026-10-02" }, { "title": "AP2 documentation", "url": "https://ap2-protocol.org/", "accessed": "2026-10-02" } ], "front_matter": { "id": "agent-that-can-buy-things", "type": "stack", "title": "Agent that can buy things", "summary": "The pieces for an agent that pays for APIs per call with x402 stablecoins and buys from merchants with controlled virtual cards, with spend limits, proof of user intent and a full audit trail.", "description": "Two payment paths cover most of what an agent needs to buy. Machine payments (x402) handle per-request charges for APIs and MCP tools from a dedicated stablecoin wallet. Card payments handle merchants, through agent-checkout protocols where they exist and a browser where they don't, using single-use or per-agent virtual cards. This stack lists a component for each job and the guardrails to put around it.", "author": "Agentica Author", "use_case": "Let an agent pay for metered APIs and tools on its own and complete merchant purchases for a user, within budgets you set and with a record of who authorized what.", "components": [ { "role": "Agent harness", "entry": "claude-agent-sdk", "why": "Runs the agent loop with tools, skills and MCP in your own app, so payment tools sit behind code you control rather than prompts. Any harness with tool calling works." }, { "role": "Machine payment protocol", "entry": "x402", "why": "Pay per request for HTTP APIs and MCP tools: the server answers 402 with a price, the agent signs a stablecoin payment and retries. SDKs default to USD stablecoins and a $1 cap per payment." }, { "role": "Agent wallet", "entry": "coinbase-agentic-wallet", "why": "A wallet built for agents, as the awal CLI with skills or as an MCP server (npx @coinbase/payments-mcp), that pays x402 services with guardrails such as a per-call maximum amount." }, { "role": "Settlement currency", "entry": "usdc", "why": "The stablecoin most x402 services price in. Fund the agent's wallet with only what it may spend, and test on Base Sepolia with faucet USDC first." }, { "role": "Service discovery", "entry": "x402-bazaar", "why": "A public index of x402-payable endpoints with prices and schemas, so the agent can find a paid API without a human signing up for keys." }, { "role": "Card credentials", "entry": "stripe-issuing-for-agents", "why": "Single-use or per-agent virtual cards with spend limits, merchant-category controls and real-time authorization webhooks, usable for programmatic checkout (MPP, UCP, Shared Payment Tokens) or in a browser." }, { "role": "Merchant checkout protocol", "entry": "agentic-commerce-protocol", "why": "OpenAI and Stripe's open checkout standard (beta); lets an agent complete a purchase through a merchant's agent-ready checkout with a delegated payment token." }, { "role": "Merchant checkout protocol (alternative)", "entry": "universal-commerce-protocol", "why": "Capability-based commerce standard over REST, MCP or A2A, covering checkout, identity linking and orders, with support for AP2 mandates." }, { "role": "Proof of user intent", "entry": "agent-payments-protocol", "why": "Signed Checkout and Payment Mandates record what the user authorized, either a specific purchase or constraints like a budget, giving merchants and you an audit trail." }, { "role": "Browser for non-agent checkouts", "entry": "browserbase", "why": "A hosted browser for merchants without an agent-checkout API, kept apart from your own machine and sessions." }, { "role": "Tracing", "entry": "langfuse", "why": "Records every tool call and payment decision so you can reconcile spend against what the agent did and why." } ], "tags": [ "payments", "agent-commerce", "x402", "stablecoins", "cards", "guardrails" ], "entries": [ "claude-agent-sdk", "x402", "coinbase-agentic-wallet", "usdc", "x402-bazaar", "cdp-x402", "stripe-issuing-for-agents", "agentic-commerce-protocol", "universal-commerce-protocol", "agent-payments-protocol", "stripe-agentic-commerce", "machine-payments-protocol", "browserbase", "langfuse" ], "sources": [ { "title": "x402 Protocol Specification v2", "url": "https://github.com/x402-foundation/x402/blob/main/specs/x402-specification-v2.md", "accessed": "2026-10-02" }, { "title": "x402 docs, Quickstart for Buyers", "url": "https://docs.x402.org/getting-started/quickstart-for-buyers", "accessed": "2026-10-02" }, { "title": "Coinbase CDP, Agentic Wallet overview", "url": "https://docs.cdp.coinbase.com/agentic-wallet/welcome", "accessed": "2026-10-02" }, { "title": "x402 docs, Bazaar (Discovery Layer)", "url": "https://docs.x402.org/extensions/bazaar", "accessed": "2026-10-02" }, { "title": "Stripe docs, Issuing for agents", "url": "https://docs.stripe.com/issuing/agents", "accessed": "2026-10-02" }, { "title": "Agentic Commerce Protocol repository", "url": "https://github.com/agentic-commerce-protocol/agentic-commerce-protocol", "accessed": "2026-10-02" }, { "title": "Universal Commerce Protocol repository", "url": "https://github.com/Universal-Commerce-Protocol/ucp", "accessed": "2026-10-02" }, { "title": "AP2 documentation", "url": "https://ap2-protocol.org/", "accessed": "2026-10-02" } ], "related": [ "pay-for-an-api-with-x402", "pay-with-x402", "agent-payment-rails", "run-untrusted-code-in-a-sandbox" ], "last_verified": "2026-10-02", "published": "2026-10-02" }, "markdown": "\n## Two ways an agent pays\n\n**Per call, in stablecoins.** For APIs and MCP tools that charge per request, the agent holds a small [USDC](https://indexagentica.com/entries/usdc/) balance in an [agent wallet](https://indexagentica.com/entries/coinbase-agentic-wallet/) and pays with [x402](https://indexagentica.com/entries/x402/): request, get 402 with a price, sign, retry. There are no accounts or API keys to create, and each payment is capped. The [x402 guide](https://indexagentica.com/guides/pay-for-an-api-with-x402/) walks through it, and the [pay-with-x402 skill](https://indexagentica.com/skills/pay-with-x402/) teaches a coding agent to do it safely.\n\n**At a merchant, by card.** For physical goods, subscriptions and anything sold through a normal checkout, the agent uses a card you control: a single-use or per-agent virtual card from [Stripe Issuing for agents](https://indexagentica.com/entries/stripe-issuing-for-agents/). Where the merchant supports an agent-checkout protocol ([ACP](https://indexagentica.com/entries/agentic-commerce-protocol/) or [UCP](https://indexagentica.com/entries/universal-commerce-protocol/)), the card travels as a delegated token and the agent never sees the number. Where it doesn't, the agent fills in the checkout in a hosted browser ([Browserbase](https://indexagentica.com/entries/browserbase/)).\n\nThe [agent payment protocols comparison](https://indexagentica.com/compare/agent-payment-rails/) explains how these protocols relate, including [MPP](https://indexagentica.com/entries/machine-payments-protocol/), which can serve both stablecoin and card payments on one endpoint.\n\n## Guardrails to set before the first purchase\n\n- **Separate money.** Give the agent its own wallet and its own cards. Fund the wallet with only what it may spend; never connect it to a treasury or a personal wallet.\n- **Caps at every layer.** x402 SDKs default to a $1 maximum per payment; keep a low cap and add a daily budget in your own tool code. On cards, use single-use cards per task, per-agent spend limits and merchant-category restrictions, and decline anything unexpected in Stripe's real-time authorization webhook.\n- **Human approval above a threshold.** Let the agent pay small metered charges on its own, and require a person to confirm purchases above an amount you choose. AP2 mandates are a standard way to record that confirmation, or the user's standing constraints for unattended purchases.\n- **Treat inputs as hostile.** Product pages, emails and API responses can carry prompt injections that try to trigger a purchase. Keep payment tools out of agents that browse untrusted content without a confirmation step, and check the recipient and amount in code, not in the prompt.\n- **Test first.** Use Base Sepolia and faucet USDC for x402, and Stripe test mode for cards, until the traces show the agent behaving as intended.\n- **Reconcile.** Trace every payment tool call with [Langfuse](https://indexagentica.com/entries/langfuse/) and match it against wallet transactions and card authorizations.\n", "raw": "---\nid: agent-that-can-buy-things\ntype: stack\ntitle: Agent that can buy things\nsummary: The pieces for an agent that pays for APIs per call with x402 stablecoins and buys from merchants with controlled virtual cards, with spend limits, proof of user intent and a full audit trail.\ndescription: \"Two payment paths cover most of what an agent needs to buy. Machine payments (x402) handle per-request charges for APIs and MCP tools from a dedicated stablecoin wallet. Card payments handle merchants, through agent-checkout protocols where they exist and a browser where they don't, using single-use or per-agent virtual cards. This stack lists a component for each job and the guardrails to put around it.\"\nauthor: Agentica Author\nuse_case: Let an agent pay for metered APIs and tools on its own and complete merchant purchases for a user, within budgets you set and with a record of who authorized what.\ncomponents:\n - role: Agent harness\n entry: claude-agent-sdk\n why: \"Runs the agent loop with tools, skills and MCP in your own app, so payment tools sit behind code you control rather than prompts. Any harness with tool calling works.\"\n - role: Machine payment protocol\n entry: x402\n why: \"Pay per request for HTTP APIs and MCP tools: the server answers 402 with a price, the agent signs a stablecoin payment and retries. SDKs default to USD stablecoins and a $1 cap per payment.\"\n - role: Agent wallet\n entry: coinbase-agentic-wallet\n why: \"A wallet built for agents, as the awal CLI with skills or as an MCP server (npx @coinbase/payments-mcp), that pays x402 services with guardrails such as a per-call maximum amount.\"\n - role: Settlement currency\n entry: usdc\n why: \"The stablecoin most x402 services price in. Fund the agent's wallet with only what it may spend, and test on Base Sepolia with faucet USDC first.\"\n - role: Service discovery\n entry: x402-bazaar\n why: \"A public index of x402-payable endpoints with prices and schemas, so the agent can find a paid API without a human signing up for keys.\"\n - role: Card credentials\n entry: stripe-issuing-for-agents\n why: \"Single-use or per-agent virtual cards with spend limits, merchant-category controls and real-time authorization webhooks, usable for programmatic checkout (MPP, UCP, Shared Payment Tokens) or in a browser.\"\n - role: Merchant checkout protocol\n entry: agentic-commerce-protocol\n why: \"OpenAI and Stripe's open checkout standard (beta); lets an agent complete a purchase through a merchant's agent-ready checkout with a delegated payment token.\"\n - role: Merchant checkout protocol (alternative)\n entry: universal-commerce-protocol\n why: \"Capability-based commerce standard over REST, MCP or A2A, covering checkout, identity linking and orders, with support for AP2 mandates.\"\n - role: Proof of user intent\n entry: agent-payments-protocol\n why: \"Signed Checkout and Payment Mandates record what the user authorized, either a specific purchase or constraints like a budget, giving merchants and you an audit trail.\"\n - role: Browser for non-agent checkouts\n entry: browserbase\n why: \"A hosted browser for merchants without an agent-checkout API, kept apart from your own machine and sessions.\"\n - role: Tracing\n entry: langfuse\n why: \"Records every tool call and payment decision so you can reconcile spend against what the agent did and why.\"\ntags: [payments, agent-commerce, x402, stablecoins, cards, guardrails]\nentries: [claude-agent-sdk, x402, coinbase-agentic-wallet, usdc, x402-bazaar, cdp-x402, stripe-issuing-for-agents, agentic-commerce-protocol, universal-commerce-protocol, agent-payments-protocol, stripe-agentic-commerce, machine-payments-protocol, browserbase, langfuse]\nsources:\n - title: x402 Protocol Specification v2\n url: https://github.com/x402-foundation/x402/blob/main/specs/x402-specification-v2.md\n accessed: 2026-10-02\n - title: x402 docs, Quickstart for Buyers\n url: https://docs.x402.org/getting-started/quickstart-for-buyers\n accessed: 2026-10-02\n - title: Coinbase CDP, Agentic Wallet overview\n url: https://docs.cdp.coinbase.com/agentic-wallet/welcome\n accessed: 2026-10-02\n - title: x402 docs, Bazaar (Discovery Layer)\n url: https://docs.x402.org/extensions/bazaar\n accessed: 2026-10-02\n - title: Stripe docs, Issuing for agents\n url: https://docs.stripe.com/issuing/agents\n accessed: 2026-10-02\n - title: Agentic Commerce Protocol repository\n url: https://github.com/agentic-commerce-protocol/agentic-commerce-protocol\n accessed: 2026-10-02\n - title: Universal Commerce Protocol repository\n url: https://github.com/Universal-Commerce-Protocol/ucp\n accessed: 2026-10-02\n - title: AP2 documentation\n url: https://ap2-protocol.org/\n accessed: 2026-10-02\nrelated: [pay-for-an-api-with-x402, pay-with-x402, agent-payment-rails, run-untrusted-code-in-a-sandbox]\nlast_verified: 2026-10-02\npublished: 2026-10-02\n---\n\n## Two ways an agent pays\n\n**Per call, in stablecoins.** For APIs and MCP tools that charge per request, the agent holds a small [USDC](https://indexagentica.com/entries/usdc/) balance in an [agent wallet](https://indexagentica.com/entries/coinbase-agentic-wallet/) and pays with [x402](https://indexagentica.com/entries/x402/): request, get 402 with a price, sign, retry. There are no accounts or API keys to create, and each payment is capped. The [x402 guide](https://indexagentica.com/guides/pay-for-an-api-with-x402/) walks through it, and the [pay-with-x402 skill](https://indexagentica.com/skills/pay-with-x402/) teaches a coding agent to do it safely.\n\n**At a merchant, by card.** For physical goods, subscriptions and anything sold through a normal checkout, the agent uses a card you control: a single-use or per-agent virtual card from [Stripe Issuing for agents](https://indexagentica.com/entries/stripe-issuing-for-agents/). Where the merchant supports an agent-checkout protocol ([ACP](https://indexagentica.com/entries/agentic-commerce-protocol/) or [UCP](https://indexagentica.com/entries/universal-commerce-protocol/)), the card travels as a delegated token and the agent never sees the number. Where it doesn't, the agent fills in the checkout in a hosted browser ([Browserbase](https://indexagentica.com/entries/browserbase/)).\n\nThe [agent payment protocols comparison](https://indexagentica.com/compare/agent-payment-rails/) explains how these protocols relate, including [MPP](https://indexagentica.com/entries/machine-payments-protocol/), which can serve both stablecoin and card payments on one endpoint.\n\n## Guardrails to set before the first purchase\n\n- **Separate money.** Give the agent its own wallet and its own cards. Fund the wallet with only what it may spend; never connect it to a treasury or a personal wallet.\n- **Caps at every layer.** x402 SDKs default to a $1 maximum per payment; keep a low cap and add a daily budget in your own tool code. On cards, use single-use cards per task, per-agent spend limits and merchant-category restrictions, and decline anything unexpected in Stripe's real-time authorization webhook.\n- **Human approval above a threshold.** Let the agent pay small metered charges on its own, and require a person to confirm purchases above an amount you choose. AP2 mandates are a standard way to record that confirmation, or the user's standing constraints for unattended purchases.\n- **Treat inputs as hostile.** Product pages, emails and API responses can carry prompt injections that try to trigger a purchase. Keep payment tools out of agents that browse untrusted content without a confirmation step, and check the recipient and amount in code, not in the prompt.\n- **Test first.** Use Base Sepolia and faucet USDC for x402, and Stripe test mode for cards, until the traces show the agent behaving as intended.\n- **Reconcile.** Trace every payment tool call with [Langfuse](https://indexagentica.com/entries/langfuse/) and match it against wallet transactions and card authorizations.\n", "html": "

Two ways an agent pays

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Per call, in stablecoins. For APIs and MCP tools that charge per request, the agent holds a small USDC balance in an agent wallet and pays with x402: request, get 402 with a price, sign, retry. There are no accounts or API keys to create, and each payment is capped. The x402 guide walks through it, and the pay-with-x402 skill teaches a coding agent to do it safely.

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At a merchant, by card. For physical goods, subscriptions and anything sold through a normal checkout, the agent uses a card you control: a single-use or per-agent virtual card from Stripe Issuing for agents. Where the merchant supports an agent-checkout protocol (ACP or UCP), the card travels as a delegated token and the agent never sees the number. Where it doesn't, the agent fills in the checkout in a hosted browser (Browserbase).

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The agent payment protocols comparison explains how these protocols relate, including MPP, which can serve both stablecoin and card payments on one endpoint.

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Guardrails to set before the first purchase

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