---
title: "FirstSales API & Developer Resources | FirstSales"
description: "FirstSales developer hub: OpenAPI 3.1 spec, an MCP server for AI agents, REST endpoints for email validation and deliverability checks, and Markdown mirrors for LLMs."
canonical: "https://firstsales.io/developers/"
---

For developers & agents

# FirstSales API & Developer Resources

FirstSales exposes its email-deliverability and outreach-quality tooling as a public REST API, an OpenAPI 3.1 spec, an MCP server for AI agents, and machine-readable Markdown mirrors of every page. Everything below is free, read-only, and requires no API key.

## OpenAPI spec

The full REST surface is described by a machine-readable OpenAPI 3.1 document, so any client generator, agent framework, or API explorer can import it directly.

* </openapi.json> — OpenAPI 3.1 spec, JSON
* </api/openapi.yaml> — the same spec, YAML

## MCP server

FirstSales runs a Model Context Protocol (MCP) server over Streamable HTTP, so any MCP client — Claude Desktop, Claude Code, or your own agent — can call these tools directly without scraping the site.

* </mcp/> — the Streamable HTTP MCP endpoint
* </.well-known/mcp.json> — discovery manifest

### Client configuration

Add this to your Claude Desktop (or any Streamable HTTP-compatible) MCP client config:

```
{
  "mcpServers": {
    "firstsales": {
      "url": "https://firstsales.io/mcp/"
    }
  }
}
```

## REST endpoints

The same capabilities exposed as MCP tools are also available as plain REST endpoints under `/api`:

* `validate_email`  
Validate an email's format, MX records, and domain existence.
* `check_disposable_email`  
Check whether an email uses a disposable/temporary domain.
* `check_catchall_domain`  
Detect whether a domain's mailbox is configured as catch-all.
* `check_domain_dns`  
Run an SPF, DKIM, DMARC, MX, blacklist, or other DNS/deliverability check.
* `check_dkim`  
Look up and validate a domain's DKIM record(s).
* `get_domain_age`  
Get a domain's registration date and age via RDAP/WHOIS.
* `get_dns_records`  
Fetch a domain's A, AAAA, MX, NS, TXT, CNAME, and SOA records.
* `analyze_spam_score`  
Score email body content for spam-trigger words and patterns.
* `analyze_subject_line`  
Analyze a subject line for spam risk and open-rate best practices.
* `analyze_cold_email`  
Analyze cold outreach copy for personalization, length, and CTA clarity.
* `list_tutorials`  
List all public FirstSales tutorials.
* `get_tutorial`  
Get the full content of one tutorial by slug.

## Markdown for agents

Every page on firstsales.io has a clean Markdown mirror for LLMs and crawlers that prefer structured text over HTML.

* </llms.txt> — full content map
* [/raw/\*.md](/raw/why.md) — Markdown mirror of any page, e.g. /raw/why.md

## Product documentation

For guides on using the FirstSales product itself (campaigns, sequences, sending, and billing), see [docs.firstsales.io](https://docs.firstsales.io).

## Support

Questions about the API or MCP server? Email [firstsales@support.communicate.so](mailto:firstsales@support.communicate.so).