Rank 2productionx402

x402 Protocol

The open HTTP 402 standard for stablecoin payments, created by Coinbase

production: Protocol v2; the @x402/* reference packages were at 2.28.0 in September 2026.

Rank: 2 of 14
Composite score: 8.6 / 10
Schemes: x402
Role: Pays 402 challenges; Charges with 402
Kind: protocol
Maturity: production
Protocol / rail: EVM / Base / Solana (USDC)
Assets: USDC, ERC-20, SPL
Networks: base, evm, solana
Custody model: Self-Custodial (EVM / Solana keypair)
Node management: Not required
MCP native: No
License: Apache-2.0
Last verified: 2026-10-15

Overview

x402 turns HTTP 402 into a payment challenge for on-chain stablecoins. In v2 the server answers with a base64-encoded PAYMENT-REQUIRED header listing accepted options — scheme, CAIP-2 network, amount in atomic units, asset and pay-to address; the client signs a payload and retries with PAYMENT-SIGNATURE, and the server reports settlement in PAYMENT-RESPONSE. v1 carried the requirements in the response body and used X-PAYMENT. Coinbase Developer Platform created the standard and publishes it as an open Apache-2.0 protocol under the x402-foundation organisation, with reference implementations in TypeScript, Python and Go; Base and Solana are supported on mainnet and testnet. It has the broadest ecosystem of any 402 scheme. The structural trade-off is settlement: payments clear at block speed with on-chain costs, so genuine sub-cent micropayments are less natural than on Lightning.

Key advantages

Open protocol (Apache-2.0) with TypeScript, Python and Go reference implementations
Stable USD unit of account — a natural fit for dollar-denominated budgets
Any ERC-20 on Base and any SPL or Token-2022 token on Solana
Many facilitators charge no facilitator fee
The broadest ecosystem of any 402 scheme

Trade-offs

Settlement is block-bound, so sub-cent payments are less natural than on Lightning
v1 and v2 use different headers (X-PAYMENT vs PAYMENT-SIGNATURE); clients must read x402Version to pick the right one
The protocol ships no MCP server itself — MCP support comes from ecosystem packages

Evaluation matrix

Custody & Sovereignty9.0
Self-custodial with exit guarantees vs. centralized/custodial risk. A 10 means the holder keeps their own keys and can unilaterally exit to the base chain; a custodial platform scores around 4.
Operational Friction8.5
Infrastructure burden. Zero nodes, channels or liquidity to manage scores a 10; running and maintaining your own Lightning node scores around 4–5.
Agent Native Support8.0
Out-of-the-box MCP server integration, typed tool calls and LLM-friendly setup. A first-party MCP server scores 9–10; a library or CLI an agent can drive scores 6–8.
Payment Rails & Assets9.0
Breadth of settlement rails and assets: Lightning for true micropayments, stablecoins for a stable unit of account, cards for mainstream reach. A single asset on a single network scores around 7.
Settlement Speed & Fees8.0
Instant sub-second settlement with near-zero overhead scores a 10. Block-bound settlement scores around 8; card-network settlement and fees score lower.
Developer DX9.0
SDK quality, documentation, maintenance and copy-paste integration speed. Alpha-stage API churn, stale releases or inconsistent docs lower the score.

Why these scores. Custody 9: the payer signs with their own keys. Friction 8.5: no node, but a facilitator and funded wallet are needed. Agent 8: no MCP server in the protocol itself; strong ecosystem MCP support. Rails 9: any ERC-20 on Base and SPL tokens on Solana. Settlement 8: block-bound but fast on Base and Solana. DX 9: mature multi-language SDKs.

Integration

Client: pay x402 endpoints

npm install @x402/fetch

Server: charge from Express

npm install @x402/express

v2 challenge — decoded PAYMENT-REQUIRED header (illustrative)

{
  "x402Version": 2,
  "accepts": [
    {
      "scheme": "exact",
      "network": "eip155:8453",
      "amount": "10000",
      "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "payTo": "0xYourReceivingAddress",
      "maxTimeoutSeconds": 60
    }
  ]
}

Best for

Services and agents that want dollar-denominated payments with a stable unit of account and the widest ecosystem support.

Sources

Every claim on this page was checked against these sources on 2026-10-15. Maturity “production” means: the vendor describes it as used or supported in production.

Machine-readable

fetch this entry as JSON

curl "https://402mcp.org/api/v1/solutions?id=x402-protocol&view=full"

or as Markdown

curl -H 'Accept: text/markdown' https://402mcp.org/solutions/x402-protocol