MCP Server

What is MCP?

The Model Context Protocol (MCP) lets AI assistants like Claude, ChatGPT, and Cursor call external tools over a standard API. Reckon’s MCP server exposes email verification and credit balance as MCP tools, so you can verify addresses and check credits from inside your AI workflow without leaving the chat. Connect once with your Reckon API key; all tools use the same key and the same rate limits as the Reckon REST API.

Endpoint: https://mcp.reckonapp.io/mcp (Streamable HTTP).

Authentication

Use your Reckon API key in the X-API-Key header.

Get or manage keys at app.reckonapp.io.

Keys must start with pk_ (public) or sk_ (secret). The same key is used for the Reckon REST API and the MCP server.

The client must send X-API-Key on every request, including each tool call. Some clients only send headers on the first request; if you see “Missing API key” when calling a tool, ensure your client sends the header on every request.

Quick setup

Reckon MCP endpoint: https://mcp.reckonapp.io/mcp (Streamable HTTP).

To add this server in your client, follow your client’s official MCP documentation and use the endpoint above with your API key in the X-API-Key header:

Client	Documentation
Claude Desktop	Getting started with MCP servers on Claude Desktop (Anthropic)
Cursor	MCP — Cursor Docs
ChatGPT	Building MCP servers for ChatGPT and API integrations (OpenAI)
Other clients	Transports (Model Context Protocol) — use Streamable HTTP

Available tools

verify_email

Verifies an email address and returns deliverability status, format validity, domain info, and risk flags (disposable, role-based, accept-all, mailbox full, plus addressing). Each successful call consumes one Reckon credit.

Input:

Field	Type	Required	Description
`email`	string	Yes	The email address to verify.

Example input:

{
  "email": "user@example.com"
}

Example success response (summary of fields):

{
  "email_address": "user@example.com",
  "status": "valid",
  "status_meta": {
    "valid_format": true,
    "domain_exists": true,
    "accept_all": false,
    "disposable": false,
    "role_based": false,
    "mailbox_full": false,
    "plus_address": false
  },
  "domain_meta": {
    "domain": "example.com",
    "mailbox_provider": "example.com"
  },
  "errors": {},
  "performed_at": "2026-02-13T14:00:00.000Z",
  "performed_in_ms": 3500,
  "requestId": "..."
}

The MCP tool returns the full API response as JSON text content.

check_credits

Returns the current email verification credit balance for the account associated with your API key. No input required.

Input: None (empty object).

Example success response:

{
  "balance": 1000,
  "asOf": "2026-02-13T14:00:00Z"
}

The MCP tool returns the full API response as JSON text content.

Rate limits

Rate limits are the same as the Reckon REST API and depend on key type:

Key type	Limits
`pk_` (public)	10 requests per key per IP per minute; 60 requests per key per minute overall.
`sk_` (secret)	500 requests per key per minute.

When you exceed the limit, the server returns a rate-limit error and may include a Retry-After value (seconds) so clients can back off and retry.

Error handling

Errors are returned as MCP/JSON-RPC errors with messages suitable for display. Underlying HTTP status from the Reckon API is reflected as follows:

Condition	Message / behavior
400 — Invalid request	“Invalid request parameters.” Check input (e.g. valid email format for `verify_email`).
401 — Invalid or missing key	“Invalid or missing API key. Get yours at https://app.reckonapp.io” Ensure `X-API-Key` is set and correct on every request.
402 — Insufficient credits	“Insufficient credits. Visit https://app.reckonapp.io to add credits to your account.” Add credits in the Reckon dashboard.
429 — Rate limit	“Rate limit exceeded.” The error may include a retry-after value; wait before retrying.
5xx — Server error	“Internal server error (status). Please try again.” Retry later or contact support if it persists.
Other 4xx	“Request failed (status). Please try again.” Check request format and parameters.

Troubleshooting

“Missing API key” or “X-API-Key header was not sent”
Your MCP client is not sending the API key on the request that invokes the tool. Configure the client so that X-API-Key is sent on every request to the MCP server, not only on the first connection.

“Invalid API key format”
The key must start with pk_ or sk_. Copy the key again from app.reckonapp.io and ensure no extra spaces or characters.

“Insufficient credits” (402)
Your account has no credits left. Add credits at app.reckonapp.io.

“Rate limit exceeded” (429)
You’ve hit the per-key (and per-IP for pk_) limits. Wait before retrying; the error may include a suggested wait time.

“Internal server error” or “Request failed (404)”
For 5xx, the Reckon API is temporarily failing; try again later. For 404, the request path or upstream API may have changed; check the docs or contact support.

Links

Reckon

Reckon App (API keys & credits)

Model Context Protocol

What is MCP?#

Authentication#

Quick setup#

Available tools#

verify_email#

check_credits#

Rate limits#

Error handling#

Troubleshooting#

Links#