x402 is an HTTP-native micropayment protocol that uses the HTTP 402 "Payment Required" status code to settle paid API calls on-chain in stablecoin in a single round-trip, with no API keys.

What is the Model Context Protocol (MCP)?

MCP is an open JSON-RPC 2.0 protocol that lets large language model agents discover and call external tools through a single standardised endpoint, removing the need for per-vendor SDKs.

What is an agent marketplace?

An agent marketplace is a venue where autonomous AI agents discover, preview, pay for, and integrate machine-payable assets (datasets, APIs, workflows, and native AI products) without a human in the transaction loop.

How do AI agents pay for APIs and data?

AI agents pay per call in stablecoin over the x402 protocol: the server returns HTTP 402 with payment requirements, the agent's wallet signs an on-chain payment proof, and the server delivers the resource in the same request.

What are USDC pay-per-call APIs?

USDC pay-per-call APIs are HTTP APIs that settle each request on-chain in USDC stablecoin instead of charging a monthly subscription or requiring a pre-issued API key.

A surveyor's table with a map, compass, and magnifier

Answers

Direct answers about agent commerce.

Short, canonical answers to the questions agent operators, dataset publishers, and AI engines ask most often about x402, the Model Context Protocol, and how machine-payable assets actually work.

What is x402?
x402 is an HTTP-native micropayment protocol that uses the HTTP 402 "Payment Required" status code to settle paid API calls on-chain in stablecoin in a single round-trip, with no API keys.
Read full answer →
What is the Model Context Protocol (MCP)?
MCP is an open JSON-RPC 2.0 protocol that lets large language model agents discover and call external tools through a single standardised endpoint, removing the need for per-vendor SDKs.
Read full answer →
What is an agent marketplace?
An agent marketplace is a venue where autonomous AI agents discover, preview, pay for, and integrate machine-payable assets (datasets, APIs, workflows, and native AI products) without a human in the transaction loop.
Read full answer →
How do AI agents pay for APIs and data?
AI agents pay per call in stablecoin over the x402 protocol: the server returns HTTP 402 with payment requirements, the agent's wallet signs an on-chain payment proof, and the server delivers the resource in the same request.
Read full answer →
What are USDC pay-per-call APIs?
USDC pay-per-call APIs are HTTP APIs that settle each request on-chain in USDC stablecoin instead of charging a monthly subscription or requiring a pre-issued API key.
Read full answer →

Looking for a definition?

The glossary has short, schema-tagged definitions for every concept Sella references: x402, MCP, ADC, Cradle, Mergekit, and more.