realtystack-mcp

A remote MCP (Model Context Protocol) connector for the RealtyStack API — U.S. real-estate data built on RentCast: property records search + single-record lookup, AVM sale-value and long-term-rent estimates with comparables, and active sale/rental listings, all in one flat /v1 JSON contract.

Upstream: https://realestate-api-kappa.vercel.app (RealtyStack REST API) — 6 tools, one per /v1 endpoint. Since the upstream deployment is metered (RapidAPI/Apify, and itself layered over RentCast's metered quota), this connector authenticates its own outbound calls with a server-side RapidAPI proxy secret (REALTYSTACK_MCP_PROXY_SECRET, sent as the X-RapidAPI-Proxy-Secret header) and applies a soft per-IP rate limit (REALTYSTACK_MCP_RATE_LIMIT, default 30 tool-calls/hour, in-memory) so this free MCP tier stays a discovery channel rather than an unmetered bypass of the paid listing — see lib/ratelimit.js.

What this is, and why it's a separate connector

RealtyStack is a plain REST API. Any HTTP client can already call it directly. This repo exists because MCP clients (Claude, ChatGPT, and other MCP-aware agents) don't consume arbitrary REST APIs — they consume MCP tools. realtystack-mcp is a thin adapter layer that:

• Exposes each RealtyStack /v1 endpoint as a discoverable, typed MCP tool (name, description, zod input schema, annotations) that an LLM can reason about and call directly, instead of having to be taught the REST surface out-of-band.
• Speaks the MCP streamable-HTTP transport at a single /mcp endpoint, so it can be registered as a connector in Claude, ChatGPT, or any other MCP client with one URL.
• Does nothing else. It has no business logic of its own — every tool call is a pass-through fetch to RealtyStack, and the JSON response RealtyStack returns is handed back verbatim as the tool result.

Authentication: none on the MCP caller side (deliberate)

RealtyStack's data has no per-user dimension — it's objective real-estate data (property records, valuation estimates, listings). There is nothing to gate per-caller, so this connector intentionally ships with:

• No OAuth, no login, no bearer tokens from the MCP client
• No Supabase / database
• No demo-vs-real account split — every caller gets the same real, live data

api/mcp.js builds a fresh, stateless McpServer per request and serves it with zero MCP-caller auth checks.

Upstream auth (outbound)

The upstream RealtyStack deployment gates every /v1/* route behind a RapidAPI proxy secret (see realestate-api/src/guard.js). This connector reaches real data by sending that same secret as the X-RapidAPI-Proxy-Secret header on its outbound fetch calls, read from the REALTYSTACK_MCP_PROXY_SECRET env var. Verified behavior: sending X-RapidAPI-Proxy-Secret passes the guard and returns real data; sending nothing returns 403 "This API is served through RapidAPI.". This is an upstream monetization detail — it does not add any auth to this connector, which still has zero MCP-caller auth by design.

Tool list

One tool per RealtyStack /v1 endpoint (from realestate-api/openapi.yaml; /api/health is intentionally not wrapped):

All 6 tools are read-only GETs, annotated { readOnlyHint: true, destructiveHint: false, idempotentHint: true, openWorldHint: true } — none of them write anything, and all of them reflect live, externally-changing real-estate data.

How it wraps realestate-api

Each tool handler does a plain fetch(\${REALTYSTACK_MCP_API_BASE_URL}${path}`, ...)against the real RealtyStack REST API (adding theX-RapidAPI-Proxy-Secret` header when configured) and returns the parsed JSON as MCP tool-result content:

{ content: [{ type: 'text', text: JSON.stringify(result, null, 2) }] }

Upstream HTTP errors (4xx/5xx) are caught and surfaced as a typed MCP error result via an asError helper rather than crashing the request.

Environment variables

Project layout

api/mcp.js       MCP endpoint (StreamableHTTPServerTransport, stateless, no caller auth)
api/health.js    GET /api/health
lib/tools.js     All 6 tool definitions (zod schemas + fetch-and-forward handlers)
lib/ratelimit.js Soft in-memory per-IP tools/call cap
local-server.js  Plain-Node http server for local dev / smoke testing (not deployed)
test/smoke.mjs   Real end-to-end smoke test (initialize, tools/list, tools/call)
vercel.json      Routes /mcp -> api/mcp.js, /health -> api/health.js
server.json      MCP registry metadata

Local development

npm install
npm run dev          # starts local-server.js on http://localhost:3900

Endpoints locally: POST http://localhost:3900/mcp, GET http://localhost:3900/health.

To hit real upstream data locally, set the proxy secret:

REALTYSTACK_MCP_PROXY_SECRET=<secret> npm run dev

Smoke test

npm run dev &                 # terminal 1
npm run smoke                 # terminal 2

test/smoke.mjs drives the running server over real HTTP/JSON-RPC and verifies:

1. GET /health returns { ok: true, ... }
2. initialize succeeds and reports serverInfo.name === "realtystack"
3. tools/list returns all 6 tools with their zod-derived JSON schemas
4. tools/call for search_properties exercises the tool end-to-end (when REALTYSTACK_MCP_PROXY_SECRET is set it asserts a real upstream result; without it, the tool-calling mechanics are still proven and the upstream's honest 403 guard response is accepted)

Deploy

Not deployed by this build (verify first). Once verified:

cd /Users/isaiahdupree/Software/realtystack-mcp
npx vercel --yes --prod

After deploy, the MCP connector URL to register in Claude/ChatGPT/any MCP client is:

https://<deployment-domain>/mcp