# base-gas-x402

> A pay-per-call gas oracle for Base mainnet that AI agents can use without an API key, a signup, or a subscription. Agents pay a fraction of a cent in USDC per request over the x402 protocol.

Base URL: https://base-gas-x402-production.up.railway.app
Payment: USDC on Base mainnet (eip155:8453) via x402, settled through the Coinbase CDP production facilitator.
Machine-readable spec: https://base-gas-x402-production.up.railway.app/openapi.json (source of truth for prices)

## Endpoints

- GET /gas ($0.005): base fee, low/medium/high priority tiers, gas price, and a cost estimate for any gasLimit. Optional: gasLimit (21000-30000000, default 21000).
- GET /gas/compare ($0.01): Base, OP Mainnet, Arbitrum One, and Ethereum ranked cheapest first. Optional: gasLimit (21000-30000000, default 21000). Chains whose RPC fails are listed under `unavailable` instead of failing the request.
- GET /gas/history ($0.012): time series plus min/max/avg/median, a `verdict` (cheap, normal, expensive, flat), `verdictNote`, and `spreadPercent`. Optional: hours (1-168).
- GET /gas/cheapest-window ($0.02): `hasDailyCycle`, a plain-language `recommendation`, hourly averages, and `savingsPercent`. Optional: hours (1-168).
- GET /health (free, no payment or wallet): sample count, hours covered, sampling interval, retention. Call this first to decide whether the history routes have enough coverage to be worth paying for.

Every paid response also embeds a `coverage` object stating how much history backs it.

## Getting started

Agent skill (recommended):
    npx skills add memosr/base-gas-skill --all --yes

Wallet (required for the paid routes):
    npx agentcash@latest onboard
    npx agentcash@latest balance

MCP server:
    npx agentcash@latest install -y
    npx skills add memosr/base-gas-skill/mcp --all --yes

Direct HTTP, free:
    curl -s https://base-gas-x402-production.up.railway.app/health

Direct HTTP, paid:
    npx agentcash@latest fetch "https://base-gas-x402-production.up.railway.app/gas?gasLimit=180000"

See the 402 challenge itself:
    curl -i https://base-gas-x402-production.up.railway.app/gas

## Useful gasLimit values

ETH transfer 21000, ERC-20 transfer 65000, NFT mint 85000, Uniswap swap 180000, contract deploy 1500000.

## What it is good at

- Five routes, each answering one question, rather than a large endpoint surface that costs an agent tokens to read.
- Free, honest coverage reporting via /health, plus a `coverage` object on every paid response.
- It reports when there is nothing to act on: a `flat` verdict from /gas/history, and `hasDailyCycle: false` from /gas/cheapest-window when timing by hour of day would save nothing on Base.
- Costs are priced per operation when you pass gasLimit, not as a raw gwei figure.
- /gas/compare degrades partially: one unreachable RPC does not fail the whole response.
- Open source and MIT licensed end to end.
- /gas at $0.005 is the cheapest current-gas endpoint in this category. This does not hold for the other routes.

## What it is not

- Not the only or the first Base gas API. Several others exist, including multi-chain toolkits covering seven chains to this one's one.
- Not the cheapest overall. Only /gas is.
- It does not promise gas savings from timing transactions on Base. Measured across two independent 15-hour windows, the spread between the cheapest and priciest hour was effectively zero.
- No usage numbers, customer counts, or traction claims. It is new.
- Single instance on Railway. No uptime guarantee and no SLA.

## Source

- API: https://github.com/memosr/base-gas-x402
- Agent skill: https://github.com/memosr/base-gas-skill
- MCP server: https://www.npmjs.com/package/base-gas-mcp