kawasekit

TypeScript SDK for stablecoin payments by AI agents. Japan-first, JPYC-native.

GA · mainnet-capable · JPYC-native. Published on npm with SLSA provenance; payment flows verified on Polygon mainnet.

pnpm add kawasekit

What it is

kawasekit gives AI agents a way to pay for things in stablecoins — without exposing developers to chain selection, gas management, or signing complexity. It is built on modern account abstraction (ERC-4337 / ZeroDev Kernel v3.1) and Japan's first regulated yen stablecoin (JPYC, classified as 電子決済手段 under 改正資金決済法).

What you can do

• Agent smart accounts + scoped session keys — a Kernel v3.1 account where the owner keeps sudo and the agent holds a policy-bounded session key (recipient allowlist + per-transfer cap + schedule window), enforced on-chain.
• Validator-agnostic issuance — issue and revoke a session key under any owner: a plain ECDSA key, or a passkey / weighted-validator sudo (the building block for non-custodial recovery — see the example).
• Gasless, sponsored payments — send JPYC as a sponsored UserOp; the agent holds no native gas token.
• Payments that say what they are for — pay an order through the Settlement contract: one UserOp, one Settled event, and an order reference the contract computes itself from what was actually paid. One order, one payment; an expired order cannot be paid; the contract holds no funds. (Unaudited; Polygon Amoy only.)
• Disposable buy-list keys — bake a buy-list (its merchants + cap + window) into a session key that can pay only through Settlement — a bare transfer is outside its scope.
• x402 micropayments — an HTTP 402 client, Hono server middleware, and a self-facilitator, with default-on reasoning-step idempotency.
• EIP-3009 EOA-payer signing — gasless transferWithAuthorization for EOA payers.
• Production plumbing — observability (Prometheus / OTLP) and a kawasekit CLI.

Examples

Two runnable example projects:

• examples/agent-x402-jpyc — a Mastra-driven Claude agent that pays a Hono paywall in JPYC over x402 (per-call micropayments).
• k0yote/kawasekit-example — ZeroDev session-key end-to-end payment, plus passkey owner & non-custodial recovery harnesses, verified on Polygon Amoy.

Documentation

Full guides, the Quick Start, and an auto-generated API reference live at kawasekit.k0yote.dev (bilingual EN / 日本語), built from docs/ with Astro Starlight. The API reference tracks the published package.

Supported chains

JPYC availability and kawasekit support are two separate axes. kawasekit ships chain configs for Polygon, Kaia, Avalanche, and Ethereum (+ their testnets) in src/chains/, each with a per-chain finality default. The x402 EOA-payer path works on every chain; the smart-account path (session keys, sponsored UserOps) is verified on Polygon.

Chain (id)	JPYC (0xE7C3…c29)	kawasekit
Polygon (137)	✅ Live	✅ config + x402 + smart-account (verified on mainnet)
Polygon Amoy (80002)	✅ Live	✅ primary testnet target
Kaia (8217) / Kairos (1001)	✅ Live¹	✅ x402 EOA path (Kairos settlement verified on-chain)
Avalanche (43114) / Fuji (43113)	✅ Live	✅ x402 EOA path
Ethereum (1) / Sepolia (11155111)	✅ Live	✅ x402 EOA path

¹ JPYC launched on Kaia in 2026-05 at the same contract address as the other chains.

Why Japan-first

• JPYC is a fully regulated yen-pegged stablecoin (電子決済手段 under 改正資金決済法), multi-chain at the same address.
• The Japanese AI startup ecosystem is actively seeking modern payment rails.

kawasekit aims to be the developer-facing layer that connects this stablecoin infrastructure to the global AI agent ecosystem.

Security

This SDK handles signing credentials and constructs financial operations. While the architecture avoids holding user funds, integration mistakes can still result in loss — audit and test thoroughly before any mainnet use. Report security issues privately to security@k0yote.dev; see SECURITY.md for the disclosure policy and docs/THREAT_MODEL.md for the layer-by-layer threat model.

Contributing

Issues, counter-examples, and discussions are the most valuable contributions today. See CONTRIBUTING.md and CODE_OF_CONDUCT.md.

License

Apache-2.0 © k0yote — includes an explicit patent grant, which matters in the account-abstraction and stablecoin space.

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Project home: kawasekit.k0yote.dev · Follow development: @k0yote