--- title: "OpenAPI reference: REST API specification | SingleFax" description: "The SingleFax OpenAPI specification for fax sends, status, inbound faxes, credits and agent payments. Download the live JSON schema or its Markdown twin." canonical_url: "https://singlefax.com/openapi" meta: "og:description": "The SingleFax OpenAPI specification for fax sends, status, inbound faxes, credits and agent payments. Download the live JSON schema or its Markdown twin." "og:image": "https://singlefax.com/images/heroes/og-product.jpg" "og:image:alt": "OpenAPI reference: REST API specification" "og:image:height": "630" "og:image:type": image/jpeg "og:image:width": "1200" "og:title": "OpenAPI reference: REST API specification | SingleFax" --- > Index of every page on this site: [llms.txt](https://singlefax.com/llms.txt) [singlefax](https://singlefax.com/) [Send & receive](https://singlefax.com/send-or-receive-fax) [For companies](https://singlefax.com/for-companies)Solutions [Pricing](https://singlefax.com/pricing) [Blog](https://singlefax.com/blog)
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[Sign in](https://singlefax.com/login) # SingleFax OpenAPI reference The live specification for the SingleFax REST API. [OpenAPI JSON](https://singlefax.com/openapi.json) [Specification as Markdown](https://singlefax.com/openapi.json.md) ## 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. [API docs and examples](https://singlefax.com/developers) [Authentication docs](https://singlefax.com/auth) [MCP server](https://singlefax.com/agents) [API versioning](https://singlefax.com/versioning) [singlefax](https://singlefax.com/) Send once. Receive when you need to. [![Get it on Google Play](https://singlefax.com/images/google-play-badge.png)](https://play.google.com/store/apps/details?id=com.monocube.singlefax) [Add to Chrome](https://chromewebstore.google.com/detail/singlefax-fax-a-document/ojpmpilgkmjcfebhpkdmmjlkbcifkkej) [SingleFax on LinkedIn](https://www.linkedin.com/company/singlefax/) [SingleFax on Facebook](https://www.facebook.com/singlefax) [SingleFax on Instagram](https://www.instagram.com/singlefax.app) [SingleFax on Threads](https://www.threads.com/@singlefax.app) [SingleFax on YouTube](https://www.youtube.com/@singlefax) [SingleFax on GitHub](https://github.com/SingleFax) ## Fax services - [Send a fax](https://singlefax.com/send-or-receive-fax?type=send) - [Receive faxes](https://singlefax.com/send-or-receive-fax?type=receive) - [Free 24-hour number](https://singlefax.com/free-fax-number) - [Lifetime number](https://singlefax.com/lifetime-fax-number) - [Number porting](https://singlefax.com/number-porting) - [Test fax](https://singlefax.com/test-fax-number) - [Company plans](https://singlefax.com/for-companies) - [HIPAA Secure](https://singlefax.com/hipaa-fax) - [Online fax](https://singlefax.com/online-fax) - [Email to fax](https://singlefax.com/email-to-fax) - [WhatsApp to fax](https://singlefax.com/whatsapp-to-fax) ## IRS filings - [All IRS filings](https://singlefax.com/irs-filings) - [EIN · Form SS-4](https://singlefax.com/get-ein) - [Form 5472](https://singlefax.com/file-5472) - [Form 7004](https://singlefax.com/file-7004) - [Form 2553](https://singlefax.com/file-2553) - [Form 2848](https://singlefax.com/file-2848) - [Form 4506-T](https://singlefax.com/file-4506-t) - [Form 8821](https://singlefax.com/file-8821) - [Form 8802](https://singlefax.com/file-8802) - [Form 8655](https://singlefax.com/file-8655) - [Form 3911](https://singlefax.com/file-3911) - [Form 8233](https://singlefax.com/file-8233) - [NY POA-1](https://singlefax.com/file-ny-poa-1) ## Tools & resources - [Free fax tools](https://singlefax.com/free-fax-tools) - [Prepare a fax PDF](https://singlefax.com/prepare-fax) - [Printable test page](https://singlefax.com/fax-test-page) - [Cover sheets](https://singlefax.com/fax-cover-sheet) - [Mobile app](https://singlefax.com/mobile-app) - [Chrome extension](https://singlefax.com/chrome-extension) - [Developers](https://singlefax.com/developers) - [AI fax agents](https://singlefax.com/agents) - [Versioning](https://singlefax.com/versioning) - [Congress fax directory](https://singlefax.com/fax/congress) - [Senate fax directory](https://singlefax.com/fax/senate) - [Governor fax directory](https://singlefax.com/fax/governors) ## SingleFax - [Pricing](https://singlefax.com/pricing) - [Blog](https://singlefax.com/blog) - [About](https://singlefax.com/about) - [Contact](https://singlefax.com/contact) - [Support](https://singlefax.com/support) © 2026 SingleFax [Privacy](https://singlefax.com/privacy-policy) [Terms](https://singlefax.com/terms-of-service) [Refunds](https://singlefax.com/refund-policy) [Report abuse](https://singlefax.com/abuse) ```json {"@context":"https://schema.org","@graph":[{"@id":"https://singlefax.com/#website","@type":"WebSite","description":"SingleFax lets you send and receive one time faxes from your phone or computer. No signup & account registration required.","inLanguage":"en","name":"SingleFax - Send & Receive one time faxes","url":"https://singlefax.com/","workTranslation":[{"@id":"https://singlefax.com/de#website"},{"@id":"https://singlefax.com/fr#website"},{"@id":"https://singlefax.com/es#website"},{"@id":"https://singlefax.com/it#website"},{"@id":"https://singlefax.com/zh-tw#website"},{"@id":"https://singlefax.com/pt-br#website"},{"@id":"https://singlefax.com/tr#website"},{"@id":"https://singlefax.com/ko#website"},{"@id":"https://singlefax.com/ja#website"},{"@id":"https://singlefax.com/ar#website"}]},{"@id":"https://singlefax.com/openapi#webpage","@type":"WebPage","description":"The SingleFax OpenAPI specification for fax sends, status, inbound faxes, credits and agent payments. Download the live JSON schema or its Markdown twin.","name":"OpenAPI reference: REST API specification","url":"https://singlefax.com/openapi","isPartOf":{"@id":"https://singlefax.com/#website"},"potentialAction":[{"@type":"ReadAction","target":["https://singlefax.com/openapi"]}]}]} ```