The Agent-Native Index

agent-native · Commerce & Payments · Verified 2026-10-27

send21

Listed on The Agent-Native Index

Payments for AI agents, without giving them your keys

Website ↗ Repo ↗ Full dossier ↗

What it does

send21 is non-custodial payment software for crypto pay links and payment drafts. An agent creates a payment request (a pay link that offers several currencies) or a draft (one payment to one receiver), priced in a crypto amount or in any of 161 fiat currencies with an exchange rate locked for 15 minutes. send21 watches the chain and reports progress by status endpoint and signed webhook until the payment confirms.

The payment itself is signed in a wallet the agent does not control: the payer’s own wallet, or the operator’s wallet through a transaction template. Assets per network: BTC on Bitcoin and Lightning; USDC, USDT, EURC, SOL and wrapped BTC on Solana; USDC, USDT, EURC, ETH and WBTC on Ethereum; USDC, EURC and ETH on Base; native USDC and ETH on Arbitrum; native USDC on Polygon.

People use the same product through the web app. The agent surface (scoped keys, MCP, idempotent create and track) is what this entry covers.

Agent-facing interfaces

How agents onboard

Interaction pattern: MCP

claude mcp add --transport http send21 https://send21.io/mcp \
  --header "Authorization: Bearer s21_..."

See the full onboarding section in the dossier.

Protocol surface

Interface Detail
REST API Authorization: Bearer s21_...; OpenAPI at https://send21.io/openapi.json; 300 requests per minute per key
MCP https://send21.io/mcp (Streamable HTTP, stateless) and https://send21.io/mcp/oauth
Webhooks POST /api/v1/webhooks; HMAC-SHA256 signatures, up to 8 attempts — docs
Python pip install langchain-send21
TypeScript npm install ai-sdk-tool-send21 ai zod (Vercel AI SDK)
Docs https://send21.io/llms.txt and https://send21.io/llms-full.txt

Verification

Last verified 2026-10-27.

Sources: