StablecoinX Paymaster — ERC-4337 reference UI

Reference and test UI for the StablecoinX paymaster service. Lets developers exercise sponsored UserOperations and ERC-20-paid gas modes against the public paymaster endpoint, useful for verifying account-abstraction integration end-to-end through the full stack of wallet, bundler, paymaster, and EntryPoint before going to production. This is a developer tool, not a consumer product, and there is no expectation that end users land here directly.

The paymaster backend is an ERC-4337 sponsorship service that supports both EntryPoint v0.8 (canonical, used by this test UI) and EntryPoint v0.7 (optional peer for clients that can't speak v0.8 yet). From this page you connect a wallet, build a UserOperation, choose between sponsor mode and ERC-20-fee mode (the paymaster pulls a stablecoin from the smart account to settle gas in fiat-equivalent terms), and submit the UserOperation through the bundler. The page also surfaces live chain configuration, current EntryPoint deposit balance, and a per-token gas estimate before signing.

The paymaster enforces a per-sender policy layer on every sponsorship request, including a rolling-hour rate cap, a daily USD spend cap, and a target-contract allowlist. Calls that exceed those limits are rejected with a structured error so the calling wallet can fall back gracefully. Default bounds are 20 sponsored operations per hour and 50 USD per day per smart-account address, configurable via the POLICY_RATE_LIMIT_PER_HOUR and POLICY_DAILY_SPEND_CAP_USD environment variables on the paymaster process (zero disables a limit).

For machine consumers, this page advertises an OpenAPI 3.x specification for the paymaster REST and RPC surface, served at openapi.json and openapi.yaml on the paymaster origin, with an interactive Swagger UI at /openapi. A robots.txt explicitly allows GPTBot, ClaudeBot, PerplexityBot, Google-Extended, and other major AI crawlers. A sitemap.xml lists the public route, and an llms.txt summarises the endpoints, contract addresses, and policy semantics for direct LLM retrieval.