AskMarcel — HVAC Technical Knowledge MCP Server

Manufacturer-sourced HVAC technical documentation for AI agents: search, diagnostics, error codes, procedures and product sheets across 126 brands and 905 models.

AskMarcel is a remote, hosted MCP server (Streamable HTTP). There is nothing to install or self-host — point your MCP client at the endpoint and authenticate. The server connects AI agents to real manufacturer documentation so answers cite the exact manual and page number instead of hallucinating.

• Endpoint: https://mcp.askmarcel.app
• Registry name: io.github.askmarcel/mcphvac
• Manifest: 1.3.1-beta.1 — 15 tools live in production
• Docs & API key: https://app.askmarcel.app/developers
• Reference: https://app.askmarcel.app/developers/reference
• Marcel Inside (B2B API / MCP): https://askmarcel.app/fr/connecteurs
• Free Developer tier: 250 API calls / month

Marcel Inside — branch it behind your bot

Use AskMarcel as Marcel Inside: plug manufacturer-sourced HVAC knowledge behind your existing chatbot, voicebot, or agent — without rebuilding your stack. Compatible with ManyChat, ElevenLabs, Voiceflow, Intercom, Claude, ChatGPT, Gemini, and custom MCP clients.

• Sales & pilot: https://askmarcel.app/fr/connecteurs (490€ pilot, Business 149€/mois HT)
• Developer sandbox: free tier — 250 calls/month at https://app.askmarcel.app/developers

Why AskMarcel

General-purpose LLMs guess at HVAC specifics — refrigerant charge, error-code meanings, wiring, fault trees. AskMarcel grounds every response in indexed manufacturer PDFs and returns the source page, so a field technician or an agent can trust and verify the answer. See HVAC-Bench for measured accuracy vs. raw LLM output.

• 126 brands · 905 models · 400,000+ error codes indexed
• Deterministic error-code lookup (not a guess)
• Strict SKU provenance (resolve_model, get_model_coverage, diagnose_v2) — no family substitution
• Sourced one-shot lookups (diagnose) and multi-turn guided troubleshooting for air-to-water heat pumps (diagnose_guided)
• LIVE Beta Harness sessions — stateful diagnostic loop with manufacturer DB lookup at session start (start_diagnostic … get_diagnostic_summary)
• FR / EN, focused on the European HVAC/RACH market

Harness session vs diagnose_guided

Harness Beta is live in production (DIAGNOSTIC_SESSIONS_PUBLIC=true). At start_diagnostic, the server looks up error codes in technical_error_codes (manufacturer DB) and journals the result — not only pack fallback maps. Active packs: pac_air_eau and pac_air_air at 0.0.1 (mutable during Beta).

Tools

The server exposes 15 tools (10 GA + 5 Beta Harness session). Full reference in docs/tools.md.

GA (10)

Beta — Harness session (5)

Stability: beta · release_channel: beta on responses · qualified HVAC professional required.

Quick start

1. Get an API key

Create a free key at https://app.askmarcel.app/developers (250 calls/month on the Developer tier). The server also supports OAuth 2.0 (PKCE + Dynamic Client Registration) for clients that discover auth automatically.

2. Connect your MCP client

Ready-to-use configs live in examples/. The general form for any Streamable HTTP MCP client:

{
  "mcpServers": {
    "askmarcel": {
      "type": "streamable-http",
      "url": "https://mcp.askmarcel.app",
      "headers": {
        "Authorization": "Bearer YOUR_API_KEY"
      }
    }
  }
}

Claude Desktop / Cursor / VS Code: see the matching file in examples/. Replace YOUR_API_KEY with your key.

3. Ask a question

Once connected, prompt naturally, e.g.:

"Daikin Altherma showing error U4 — what does it mean and how do I clear it?"

The agent calls resolve_model / diagnose_v2 (or get_error_code / diagnose) and returns the cause, the fix steps, and the source manual page — or an explicit abstention when no exact manual exists.

For a full field diagnostic loop on a heat pump, use start_diagnostic → respond_to_diagnostic → close_diagnostic (see skill hvac-harnais-session).

MCP vs Chat API

AskMarcel exposes two separate integration surfaces — do not mix their protocols:

The MCP server does not use the AI SDK chat stream (text-delta, data-* parts). If you build a custom agent with the Vercel AI SDK, use MCP tools via JSON-RPC — not the web chat endpoint.

Authentication

Two supported methods (details in docs/authentication.md):

1. API key (Bearer): Authorization: Bearer YOUR_API_KEY
2. OAuth 2.0: discovery via https://mcp.askmarcel.app/.well-known/oauth-protected-resource

Claude Skills

The skills/ folder contains ready-to-use Agent Skills that wrap these tools into HVAC workflows:

• hvac-error-lookup — turn a brand + error code into a sourced explanation and fix.
• hvac-diagnostic — one-shot symptom lookup with citations (diagnose).
• hvac-guided-diagnosis — multi-turn guided troubleshooting for air-to-water heat pumps (diagnose_guided).
• hvac-harnais-session — Beta Harness session loop (start_diagnostic … close_diagnostic).

REST API SDK

For custom agents that call the REST API directly (not MCP), use the npm package @askmarcel/sdk — includes Harness session methods (startDiagnosticSession, respondToDiagnosticSession, …), guidedTurn() for POST /v1/diagnostic/turn, plus resolveModel() / getModelCoverage() / V2 diagnose.

Links

• MCP endpoint — https://mcp.askmarcel.app
• Developer portal & API key — https://app.askmarcel.app/developers
• API reference — https://app.askmarcel.app/developers/reference
• Marcel Inside (B2B) — https://askmarcel.app/fr/connecteurs
• Templates — https://app.askmarcel.app/templates
• Official MCP Registry — io.github.askmarcel/mcphvac
• Website — https://askmarcel.app

License