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SingleFax OpenAPI reference

The live specification for the SingleFax REST API.

OpenAPI JSONSpecification as Markdown

REST API integration

The specification describes requests, responses, security schemes and errors for the public API. Use it with OpenAPI tooling to generate a client, validate requests or explore the available operations. Send the original document; SingleFax converts supported files before transmission.

Authentication and payments

Backend API-key sends use prepaid credits. Chat clients connect to the MCP server with OAuth. Machine payment endpoints issue HTTP 402 challenges for supported payment methods. Each operation in the specification documents its requirements.

Official CLI and language examples

The official package is the npm CLI @singlefax/cli. The developer portal also has REST examples for JavaScript, Python, Go and PHP. Those examples use standard HTTP clients; SingleFax does not currently publish Python, Go or Ruby SDK packages.