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API Access

Free Sumline API key

Call Sumline's calculators from your own code, agent, or any MCP-capable client via our MCP endpoint. Free tier: 5 calls per day. No credit card required.

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How to use your key

Send it as the x-api-key header to https://usesumline.com/mcp. Any client that supports remote MCP servers and custom request headers can use this API-key path.