x402-payable API platform on Base offering data, AI, finance, and utility endpoints at $0.02/request.
What it does
lowpaymentfee.com is an x402-enabled API platform that exposes a broad set of endpoints across four categories: Data & Analytics (metrics, reports, data 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 via the x402 protocol — no API keys, no rate limits, and no signup required.
The specific endpoint at `/api/v1/carts/21` 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), which equals $0.02 given USDC's 6 decimals. Payment is made via the `exact` scheme to the specified payTo address, with a 300-second timeout. The endpoint accepts HTTP POST requests and returns `application/json`.
Documentation beyond the landing page is extremely sparse — the /docs, /api, /pricing, and /README pages all render only a "Connect wallet" prompt with no further content. There is no OpenAPI spec, no request/response schema documentation, and no usage examples available. The purpose of the `/api/v1/carts/21` endpoint specifically is unclear; it does not correspond to any of the advertised API categories on the homepage. Prospective users should be aware that the actual functionality behind this endpoint is undocumented.
Capabilities
Use cases
- —Agent-driven data retrieval with per-call USDC micropayments
- —On-demand AI inference (sentiment, summarization, classification) without API key management
- —Fetching real-time crypto gas estimates or token quotes via x402
- —Geocoding or data conversion as a utility service with no subscription
Fit
Best for
- —Developers or agents wanting zero-signup, pay-per-use API access
- —x402-compatible agents that can settle USDC on Base
- —Prototyping workflows that need cheap, frictionless API calls
Not for
- —Users who need detailed API documentation or guaranteed SLAs
- —High-volume production workloads requiring rate-limit guarantees or bulk pricing
- —Users without a Base-compatible USDC wallet
Quick start
curl -X POST https://lowpaymentfee.com/api/v1/carts/21 \
-H "Content-Type: application/json" \
-H "X-PAYMENT: <x402-payment-token>" \
-d '{}'Endpoint
Quality
The endpoint is live and returns a valid x402 402 challenge, confirming pricing and payment details. However, documentation is essentially nonexistent beyond the landing page listing. The specific /api/v1/carts/21 endpoint is not described among the advertised APIs, there is no OpenAPI spec, no request/response schema, and no examples. This is effectively a stub listing.
Warnings
- —The /api/v1/carts/21 endpoint does not match any of the advertised API paths on the homepage — its actual functionality is unknown.
- —All documentation pages (/docs, /api, /pricing, /README) render only 'Connect wallet' with no usable content.
- —No OpenAPI spec, no request/response schema, and no usage examples are available.
- —The platform lists many endpoints on its homepage but none have documented input/output schemas.
Citations
- —All endpoints are priced at $0.02 per request with no API keys, no rate limits, and instant access on Base network.https://lowpaymentfee.com
- —The x402 challenge for /api/v1/carts/21 specifies maxAmountRequired of 20000 base units of USDC (asset 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913) on Base with a 300-second timeout.https://lowpaymentfee.com/api/v1/carts/21
- —Available API categories include Data & Analytics, AI & Machine Learning, Finance & Web3, and Infrastructure.https://lowpaymentfee.com
- —Documentation pages /docs, /api, /pricing, /README all show only 'Connect wallet' with no further content.https://lowpaymentfee.com/docs