x402-gated API platform on Base offering data, AI, finance, and utility endpoints at $0.02/request.
What it does
lowpaymentfee.com is an x402-protocol API marketplace that exposes a variety of endpoints across four categories: Data & Analytics (metrics, reports, export, insights), AI & Machine Learning (sentiment analysis, text summarization, classification, embeddings), Finance & Web3 (price feeds, exchange rates, token quotes, gas estimates), and Infrastructure utilities (geocoding, validation, conversion, generation). All endpoints are priced at $0.02 per request, payable in USDC on the Base network with no API keys, no rate limits, and no minimum commitments.
The specific endpoint at `/api/v1/inbox/138` is listed as "Premium API Access" and returns a valid x402 challenge with a `maxAmountRequired` of 20,000 base units of USDC (0x8335…2913 on Base). Since USDC uses 6 decimals, this equals $0.02 per call, consistent with the site-wide pricing. Payment is made via the x402 exact scheme, with a 300-second timeout. The endpoint accepts HTTP POST requests and returns `application/json`.
Documentation beyond the landing page is sparse — the /api, /pricing, and /README pages all resolve to a wallet-connect prompt with no additional content. There is no OpenAPI spec, no request/response schema documentation, and no usage examples available from the crawl. The purpose of the `/api/v1/inbox/138` path specifically (as opposed to the named endpoints like `/api/v2/ai/sentiment`) is unclear; it may be a generic or catch-all premium endpoint. Without further documentation, the exact input parameters and response format cannot be determined.
Capabilities
Use cases
- —Calling AI inference endpoints (sentiment, summarization, classification, embeddings) without API key management
- —Fetching real-time crypto price feeds and gas estimates with per-request micropayments
- —Running geocoding or data validation utilities on a pay-per-use basis
- —Exporting analytics data or generating reports without subscription commitments
- —Agent-driven workflows that need low-friction, wallet-authenticated API access
Fit
Best for
- —AI agents and bots that can settle x402 payments autonomously on Base
- —Developers who want pay-per-request access without API key signup
- —Low-volume or bursty workloads where subscription pricing is wasteful
Not for
- —High-volume production workloads needing SLAs, rate guarantees, or dedicated support
- —Users without a Base-compatible wallet or USDC holdings
- —Applications requiring detailed API documentation or OpenAPI specs before integration
Quick start
curl -X POST https://lowpaymentfee.com/api/v1/inbox/138 \
-H "Content-Type: application/json" \
-H "X-PAYMENT: <x402-payment-token>" \
-d '{}'Endpoint
Quality
The endpoint is live and returns a valid x402 challenge with clear pricing, but there is no OpenAPI spec, no request/response schema, no usage examples, and the specific purpose of /api/v1/inbox/138 is undocumented. The landing page lists many endpoints but provides no detail on inputs or outputs.
Warnings
- —No OpenAPI or schema documentation available for any endpoint
- —The /api, /pricing, and /README pages return only a wallet-connect prompt with no content
- —The specific path /api/v1/inbox/138 ('Premium API Access') does not correspond to any of the named endpoints on the landing page — its exact function is unknown
- —No request body schema or response examples are documented anywhere in the crawl
Citations
- —All endpoints are priced at $0.02 per request with no API keys, no rate limits, and instant access on the Base networkhttps://lowpaymentfee.com
- —The x402 challenge returns maxAmountRequired of 20000 base units of USDC (asset 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913) on Base with a 300-second timeouthttps://lowpaymentfee.com/api/v1/inbox/138
- —Available endpoint categories include Data & Analytics, AI & Machine Learning, Finance & Web3, and Infrastructurehttps://lowpaymentfee.com