FirstSales API & Developer Resources

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 — 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.