SENTINEL Washington Real Estate

SENTINEL Washington Real Estate MCP

Source-dated Washington property evidence and transaction math for software and compatible AI assistants. One REST and MCP service combines supported county facts, permit and site context, REET, seller calculations and bounded research packets. It complements licensed MLS data; it does not replace an MLS feed.

Developer guide · Console · OpenAPI · Developer terms

Use it in Claude or ChatGPT

For Washington real estate agents. Paste one address into your assistant and sign in once; no keys or code.

• Claude (claude.ai, Desktop or mobile): Settings, Connectors, Add custom connector. Name it Sentinel and paste https://app.sentineliq.net/api/v1/mcp.
• ChatGPT (with developer mode turned on in settings): create a new app, paste the same address and choose OAuth.

The REET, net-sheet and NWMLS deadline calculators work straight away without an account. The first time you ask for property, permit or market data, your assistant shows a Connect button: sign in to Sentinel (or create an account), approve the connection, and the assistant carries on. The first 7 days are free with no card; after that, Sentinel Connect is $29 a month and can be cancelled any time from the console, where you can also disconnect an assistant.

Try asking: "What's the REET on a $750,000 sale in King County?", "Pull the permit history for 123 Main St, Bellingham", "How have home prices in King County changed?" or "Build a seller net sheet at $725k and $750k with a $420k payoff."

Try without an account

curl -s https://app.sentineliq.net/api/v1/public/reet \  -H 'Content-Type: application/json' \  -d '{"sale_price":750000,"county":"king"}'

Worked example: $8,655 state REET + $3,750 county-level local REET + $5 technology fee = $12,410 estimated total. The full response includes the tax bands, scope, assumptions, disclaimer and attribution. This is an estimate for a standard residential transfer; verify the location code and applicable rules.

Tools

The three public REST calculators use /api/v1/public/ instead. Tools do not create deals, change CRM records or send messages. Successful keyed calls update the account's usage ledger.

REST field names use snake_case. MCP arguments use camelCase; inspect tools/list for the exact schema. MCP output retains the REST response's field names.

Connect

Public URL: https://app.sentineliq.net/api/v1/mcp/public Keyed URL: https://app.sentineliq.net/api/v1/mcp

The public connection exposes three calculators. The keyed connection lists all seventeen tools and answers the three calculators without credentials. For the other tools it accepts either:

• OAuth sign-in (Claude, ChatGPT and other clients that support MCP authorization): the server returns 401 with a WWW-Authenticate header pointing to /.well-known/oauth-protected-resource. Sentinel's authorization server supports PKCE (S256), dynamic client registration and client ID metadata documents. Each approved connection appears in the console as "Connected app: name" and can be revoked there.
• An API key: Authorization: Bearer agk_... set in your client's protected credential settings. Keys belong on a server or in secure local configuration, never shared source files.

Cursor

Use .cursor/mcp.json:

{  "mcpServers": {    "sentinel": {      "url": "https://app.sentineliq.net/api/v1/mcp/public"    }  }}

VS Code

Use .vscode/mcp.json. VS Code uses servers and an explicit transport type:

{  "servers": {    "sentinel": {      "type": "http",      "url": "https://app.sentineliq.net/api/v1/mcp/public"    }  }}

Claude Code

claude mcp add --transport http sentinel https://app.sentineliq.net/api/v1/mcp/public

Other clients must support a remote HTTP MCP server. Availability and protected header configuration vary by client and plan. No universal compatibility claim is made. The optional Claude Desktop example uses a third-party stdio bridge; review that dependency before using it.

Protocol behavior

Server version: 1.5.1. Supported protocol revisions are 2026-07-28, 2025-06-18 and 2025-03-26. Transport is stateless HTTP POST with JSON responses; a legacy HTTP+SSE server is not provided.

Current 2026-07-28 clients use server/discover. Requests include the MCP-Protocol-Version and Mcp-Method headers; tools/call also includes Mcp-Name. The body params._meta must carry io.modelcontextprotocol/protocolVersion and io.modelcontextprotocol/clientCapabilities. Header and body values must agree.

Legacy 2025-03-26 and 2025-06-18 clients use initialize and send the negotiated MCP-Protocol-Version header thereafter. The supported structured-result revisions return structuredContent and outputSchema alongside text content. Inspect the negotiated capabilities rather than assuming a client version.

Initialize, discovery and notifications do not consume successful-call quota. Business failures appear as result.isError with a text error; protocol errors use JSON-RPC errors. Preserve X-Request-Id when contacting support.

Research one property with evidence

The wa_research_packet tool resolves one supported Washington property and returns source-backed facts, calculations, conflicts, unknowns, follow-up questions and field-level references in a single bounded response. Compact and full projections preserve the same claims, qualifications and required notices. Optional coordinate context remains a separate point observation; it is never treated as proof of a parcel match. A useful partial packet counts as one successful call, while unavailable or ambiguous research does not.

wa_property_changes reads the permit versions Sentinel has actually captured. It distinguishes agency event dates from Sentinel observation times and treats the first capture as a baseline, not as a newly observed change. History begins at that first immutable capture and can be incomplete.

Build a seller packet

A data-independent first request compares two prices with a known payoff and explicitly no seller credits:

{  "county": "king",  "scenarios": [    {"label": "Conservative", "sale_price": 725000, "mortgage_balance": 420000, "concessions": 0},    {"label": "Target", "sale_price": 750000, "mortgage_balance": 420000, "concessions": 0}  ]}

POST this body to /api/v1/agent-api/v1/seller-packet with your bearer key. The response includes report_markdown, structured scenarios, section statuses, gaps, generation time and provenance. Property and market inputs are optional; while sale-price snapshots are paused, a market input is answered from licensed market trends in the market_trends field. The packet is not an appraisal or CMA and does not fetch comparable sales.

Omitted or null mortgage_balance and concessions mean unknown. Explicit 0 means no payoff or seller credits. Preserve each proceeds label and its mortgage_payoff_known and concessions_known flags. Scenario deltas include comparable and a nullable amount; a null difference is not zero. The response's fully_comparable flag tells you whether every scenario has a known payoff and known seller credits.

Offer comparisons share a single payoff. When credits are known for every offer, differences can still be compared without that payoff, but comparison_basis is before_mortgage_payoff rather than net_proceeds. Unknown credits suppress the offer spread and highest-proceeds labels. Do not present a proceeds amount before unknown costs as final seller cash.

The Python and curl examples demonstrate calls without sending messages or changing customer records. They will make network requests when you run them.

Coverage and data interpretation

• County property records cover King, Pierce, Snohomish and Whatcom only.
• REET local-rate assumptions cover eleven counties; that is not eleven-county property coverage.
• Historical cached building attributes may include earlier enrichment and are not independently verified field by field. interior_provenance_status is not_recorded when historical source tracking was not recorded; preserve provenance_note alongside the attributes. A county attribution is not proof of each building attribute's source.
• Known portal backfills are omitted (portal_suppressed). Current listing overrides are replaced with cached property values, which carry the same historical provenance limitation. Missing or unavailable facts stay null.
• Listing status, price and related fields are included only for a matched licensed listing already on file. Null means no licensed listing on file, not that a property is off market.
• Listing links, photos and portal automated valuations are not returned.
• Owner identity, mailing addresses, absentee classifications and equity estimates are excluded. No list export, bulk enumeration or lead feed exists.
• Recorded sale history (wa_sale_history) for one Pierce or Snohomish County parcel: up to three years of county assessor sale dates and prices, with validity codes and no buyer, seller or owner names.
• Market trends (wa_market_trends) answer for a Washington ZIP, county, city (as its ZIP codes) or metro from sources whose reuse terms are recorded: the FHFA House Price Index (an appreciation index, not a dollar price) and, once its terms are confirmed, Realtor.com monthly listing inventory (asking prices, not closed sales). Each block names its publisher, period, source file hash and required notice. Areas without licensed figures are free.
• Sale-price market snapshots (wa_market_snapshot) are paused while their source's terms are reviewed. Calls return an unavailable error and are not charged.
• Carry through attribution entries marked required and all relevant assumptions and disclaimers. The developer terms apply to source data and API use; the example-code license does not grant additional data redistribution rights.

Access and limits

Public REST calculators: 60 requests/minute and 5,000/day per public client IP. Public MCP: 60 requests/minute and 500/day per public client IP. Keyed tools: 60 requests/minute per key; 2,000 successful calls per rolling 24 hours per account, shared across REST and MCP. Five active keys per account. New accounts get a free 7-day trial with no card, up to 200 successful calls a day. Start one with just an email at https://sentineliq.net/mcp; the key it shows goes in the Authorization header for agents that cannot sign in. After the trial, calls return TRIAL_ENDED with a link to the $29 Sentinel Connect checkout. Failed requests, validation failures, not-found misses and whoami checks do not count. GET /api/v1/agent-api/v1/whoami is an unmetered identity/usage check.

Existing paid accounts retain their API access and published account allowance. The current entry points are the 7-day free trial, Sentinel Connect and the integration pilot.

Sentinel Connect, $29 a month, is for agents using Sentinel inside Claude or ChatGPT: the full keyed catalog with the account allowance above, renewing monthly until cancelled from the console.

The optional $250, 30-day integration pilot covers one agreed workflow, one developer account with up to five integration keys, setup help and a success check. It is a one-time payment with no automatic renewal. Checkout is shown only when payment setup is available; otherwise contact the founder before the pilot starts. These are integration keys, not user seats; published per-account limits still apply. Contact [email protected].