AskMarcel — HVAC Technical Knowledge MCP Server

Name: AskMarcel HVAC Technical Knowledge
Author: askmarcel

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`

Surface	Use when	Quota
Harness session (`start_diagnostic` …)	Multi-turn field diagnostic on PAC Air/Eau or PAC Air/Air with hypotheses, discriminating `next_action`, technician journal	Once at session creation
`diagnose_guided`	Legacy guided loop for PAC Air/Eau only — server-sealed state via `continuation`	Per turn
`diagnose_v2`	One-shot strict SKU lookup	Per successful call
`diagnose`	One-shot lookup without SKU gate	Per successful call

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)

Tool	What it does
`search_technical_docs`	Semantic search over technical documentation (≤10 excerpts). Filter by `brand`, `model`, `error_code`.
`get_procedure`	Retrieve a full procedure by `chunk_id`.
`get_error_code`	Deterministic lookup by `brand` + `error_code` (optional `model`).
`get_product_sheet`	Product sheet: specs, composition, frequent error codes, by `brand` + `model`.
`get_pdf_page_snapshot`	Signed, 5-minute URL to a specific PDF page (`document_id` + `page`).
`diagnose`	One-shot sourced lookup from a symptom or error code (excerpt + steps + citation).
`diagnose_v2`	Same lookup with strict SKU provenance. Abstains (`diagnostic: null`) if no approved exact-model manual exists.
`resolve_model`	Resolve `brand` + `model` to a canonical SKU. Exact or alias only — never a series LIKE.
`get_model_coverage`	Documentary flags for a resolved SKU: `exact_manual`, `error_code_covered`, `market_verified`.
`diagnose_guided`	Multi-turn guided troubleshooting for air-to-water heat pumps (legacy; quota per turn).

Beta — Harness session (5)

Tool	What it does
`start_diagnostic`	Open a stateful Harness session. Manufacturer error-code lookup at start. Quota on creation.
`get_diagnostic`	Read current session projection (`hypotheses`, `next_action`, fault code).
`respond_to_diagnostic`	Append typed observation, measurement, or technician assessment.
`close_diagnostic`	Close session with optional reason (verification not required).
`get_diagnostic_summary`	Deterministic exportable summary from the session journal.

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:

Surface	Endpoint	Protocol	Use case
MCP server (this repo)	`https://mcp.askmarcel.app`	JSON-RPC Streamable HTTP (`tools/call`)	Connect Claude, Cursor, VS Code, or any MCP client to HVAC tools
Chat API (web / mobile / extension)	`https://app.askmarcel.app/api/chat`	AI SDK v5 SSE (`UIMessageStream`)	Full conversational UI with streaming, tools, and document blocks

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):

API key (Bearer): Authorization: Bearer YOUR_API_KEY
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.

License

Code and content in this repository (documentation, examples, skills) are released under the MIT License. The AskMarcel hosted service and its underlying data are proprietary and governed by the AskMarcel terms.

🇫🇷 En français

AskMarcel est un serveur MCP distant et hébergé (Streamable HTTP) qui connecte les agents IA à la documentation technique HVAC/RACH sourcée constructeur. Rien à installer : on pointe son client MCP sur l'endpoint et on s'authentifie. Chaque réponse cite le manuel et la page exacte plutôt que d'halluciner.

Endpoint : https://mcp.askmarcel.app
Nom registre : io.github.askmarcel/mcphvac
Manifeste : 1.3.1-beta.1 — 15 outils en production
Doc & clé API : https://app.askmarcel.app/developers
Marcel Inside (B2B) : https://askmarcel.app/fr/connecteurs
Tier Developer gratuit : 250 appels / mois
Couverture : 126 marques · 905 modèles · 400 000+ codes erreur indexés

Marcel Inside — branchez la base AskMarcel derrière votre chatbot, voicebot ou agent existant. Pilote 490€ · Business 149€/mois HT · tier Developer gratuit pour tester.

15 outils : 10 GA (search_technical_docs, get_procedure, get_error_code, get_product_sheet, get_pdf_page_snapshot, diagnose, diagnose_v2, resolve_model, get_model_coverage, diagnose_guided) + 5 session Harnais Beta (start_diagnostic, get_diagnostic, respond_to_diagnostic, close_diagnostic, get_diagnostic_summary).

Harnais Beta LIVE : lookup DB fabricant (technical_error_codes) au start_diagnostic, packs pac_air_eau / pac_air_air 0.0.1, quota à la création de session seulement. Distinct de diagnose_guided (guidé legacy PAC Air/Eau, quota par tour).

Skills : lookup code erreur, diagnostic one-shot, guidé PAC, session Harnais — voir skills/.

SDK REST (npm) : @askmarcel/sdk — sessions Harnais + guidedTurn() + API v2.

Connexion rapide : créez une clé sur https://app.askmarcel.app/developers, puis utilisez une des configs du dossier examples/ (Claude Desktop, Cursor, VS Code). Remplacez YOUR_API_KEY par votre clé.

MCP vs Chat API : ce dépôt documente le serveur MCP (JSON-RPC sur mcp.askmarcel.app). Le chat web/mobile utilise une API distincte (SSE AI SDK v5 sur /api/chat) — les deux protocoles ne sont pas interchangeables.

Détails des outils : docs/tools.md · Authentification : docs/authentication.md.

AskMarcel HVAC Technical Knowledge