Start in the sandbox with free trial credits, or skip the account entirely with x402 for single-claim calls. Paid audit, diff, covenant, and proof workflows draw from API-key credits.
Free trial credits, no card. Use it against the demo, MCP tools, and the local CLI, then top up when you need volume.
x402 clients verify single claims with no signup — $0.005 per decisive call, settled in USDC on Base.
Open x402 discovery ↗curl -X POST https://numproof.com/verify \
-H "Authorization: Bearer vk_…" \
-H "Content-Type: application/json" \
-d '{"claim":"(R-C)/R == 1 - C/R"}'