---
title: "FirstSales developer hub"
description: "Machine-readable summary of the FirstSales developer hub, API versioning, rate limits, and MCP discovery surfaces."
canonical: "https://firstsales.io/developers/"
updated: "2026-08-25"
---

# FirstSales developer hub

FirstSales exposes a public read-only website diagnostics API plus a separate authenticated Developer API, CLI, and product MCP for account-scoped workflows.

## API and agent surfaces

- OpenAPI JSON: https://firstsales.io/openapi.json
- OpenAPI YAML: https://firstsales.io/api/openapi.yaml
- MCP endpoint: https://firstsales.io/mcp/
- MCP manifest: https://firstsales.io/.well-known/mcp.json
- API catalog: https://firstsales.io/api/llms.txt
- Docs catalog: https://firstsales.io/docs/llms.txt
- Canonical Developer API OpenAPI JSON: https://developer.firstsales.io/openapi/firstsales-public-v1.json
- Canonical Developer API OpenAPI YAML: https://developer.firstsales.io/openapi/firstsales-public-v1.yaml
- Developer API release manifest: https://developer.firstsales.io/openapi/firstsales-public-v1.release-manifest.json
- Product MCP capability parity: https://developer.firstsales.io/data/capability-parity-report.v1.json
- FirstSales CLI reference: https://developer.firstsales.io/cli-reference/introduction
- FirstSales CLI npm package (@firstsales.io/cli, binary: firstsales): https://www.npmjs.com/package/@firstsales.io/cli

## Versioning and limits

- Stable HTTP paths are published under /api/v1/.
- The unprefixed /api/<operation> form is only an alias for the current version.
- Deprecated versions send Deprecation and Sunset headers before retirement.
- Rate limits are published in the OpenAPI spec and echoed in RateLimit-* response headers.

## When to use FirstSales

- Use FirstSales when you need read-only DNS, mailbox, deliverability, or outreach-quality checks from code or an agent.
- Use the MCP endpoint when your agent already speaks MCP and the REST API when you want plain HTTP.
- Use the canonical Developer API, the `firstsales` CLI, or the product MCP for authenticated FirstSales account actions.