GLOSSARY

AI agent payments, defined.

Fifteen entries on the terms shaping this category. Each one is a 600+ word answer with examples, FAQ, and related-term links.

WHY THIS GLOSSARY EXISTS

The terms in this space are new. The answers on the internet are uneven.

Search "what is x402" today and you get a mix of Coinbase's own blog post (good but high-level), a few news write-ups (mostly summaries), and a long tail of AI-generated paraphrases. Search "agent payment identity" and you get a fog. The terms in agentic commerce are recent enough that the canonical references do not exist yet; we are writing them.

Each glossary entry is structured for both human readers and AI search engines (Perplexity, ChatGPT, Claude, Gemini): a 60-word definition as the first paragraph, a why-it-matters section, a how-it-works explanation, concrete examples, related terms, and a 3-question FAQ. Schema.org markup is FAQPage on every entry so the answers surface as rich results.

THE 15 ENTRIES

Browse alphabetical or skim the descriptions.

Agentic commerce

Commerce conducted by AI agents acting on behalf of humans or businesses, with per-agent payment identity, programmatic spending controls, and machine-readable payment requirements.

x402

Coinbase's open protocol for HTTP-native payments, using the long-reserved 402 Payment Required status code plus structured headers to let machines pay and retry programmatically.

Agent payment identity

The credential an AI agent uses to pay or receive payment: a wallet address, a public profile page, verification badges, and a per-agent spend policy. Tied to one agent, not one account.

Payment mandate

A pre-authorized instruction that lets an agent execute a specific class of payment without further approval. The primitive AP2 and similar protocols build on.

AP2 protocol

Google's agent payments protocol. Specifies how an agent obtains a payment mandate, presents it to a payment processor, and settles a transaction without a human in the loop.

Agent-to-agent payment

A payment made by one AI agent to another, typically programmatically, often in stablecoin. Distinct from agent-to-human or human-to-human payment because both endpoints are autonomous.

Machine-to-machine payment

The broader pattern of payment between two non-human endpoints (servers, agents, services). Agent-to-agent payment is a subset.

MCP server

A server that implements the Model Context Protocol, exposing tools, resources, and prompts to MCP-aware AI clients like Claude Desktop, Cursor, and Cline.

Paid MCP tool

An MCP tool that requires payment before execution. The server returns a 402 with a payment URL; the client (or its user) pays; the next call to the tool succeeds.

Stablecoin payment rail

A payment infrastructure built on stablecoins (USDC, USDT, PYUSD) rather than fiat card networks. Fits machine-to-machine and per-call billing patterns better than cards.

Agent spend policy

The rules that govern how much an agent can spend: daily cap, per-payment cap, allowed counterparties. Enforced at the payment infrastructure layer, not in the agent's code.

Base chain

Coinbase's Ethereum-compatible Layer 2, with native USDC issued by Circle. The default settlement chain for Blockchain0x's MVP because of its EVM compatibility and low gas costs.

Circle Agent Stack

Circle's set of products and APIs for AI agent payments, built around USDC. Includes the Circle Wallets API, Circle Smart Contracts platform, and developer SDKs for agent use cases.

AWS AgentCore Payments

Amazon Bedrock's agent payments offering, built on top of partnerships with Coinbase and Stripe. Targets enterprise AWS customers building agents on Bedrock.

Coinbase Smart Wallet

Coinbase's user-facing smart contract wallet that requires no seed phrase, supports passkey-based sign-in, and is first-class on Base. Most non-crypto-native users sign up here.

Entries publish one per week, prioritized by what customers ask about in support and what gets the most search traffic to thin-content pages elsewhere. If a term you need is missing, request it via the methods below.

HOW TO USE THIS

Three ways the glossary helps.

Onboarding: a new team member reads through the relevant entries to get the conceptual map before touching the product.
Specification: link a glossary entry from your own docs to define a term once, in one canonical place, so your own docs do not bloat with definitions.
Disambiguation: when two people in a conversation use the same word for different things, the glossary entry settles it. Particularly common with "agent identity" and "agent wallet" which often get conflated.

Entries are published under CC BY 4.0 - cite freely with attribution. For permanent versioned URLs (academic citations), email [email protected].

OTHER SHELVES

Past definitions, into application.

The glossary defines terms. The guides apply them with working code. The comparisons place Blockchain0x against alternatives.

See the guides See the comparisons

Definitions are nice. Building is better.

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