diff --git a/voice-to-mermaid/README.md b/voice-to-mermaid/README.md
index 6c2b94d..e693236 100644
--- a/voice-to-mermaid/README.md
+++ b/voice-to-mermaid/README.md
@@ -66,18 +66,31 @@ WebSocket /ws/mermaid
 
 ---
 
-## Environment Variables
+## Configuration
 
-### Backend (`backend/.env`)
+### `backend/config.yaml` — non-secret settings
+
+Edit this file to change model names, Whisper settings, prompt path, and model filter.
+It is volume-mounted in Docker, so changes take effect on restart without rebuilding.
+
+| Key | Default | Description |
+|---|---|---|
+| `ollama.default_model` | `qwen3:8b` | Ollama model for diagram generation |
+| `ollama.model_filter` | _(list)_ | Model name prefixes shown in the UI picker |
+| `openai.model` | `gpt-4o-mini` | OpenAI-compatible model name |
+| `whisper.enabled` | `false` | Set `true` after installing `requirements.stt.txt` |
+| `whisper.model` | `medium.en` | Whisper model size |
+| `whisper.device` | `auto` | `auto` / `cpu` / `cuda` |
+| `paths.prompt` | `prompts/mermaid.txt` | Path to LLM prompt template |
+| `paths.log_dir` | `data/logs` | Directory for generation logs |
+
+### Backend (`backend/.env`) — secrets only
 
 | Variable | Default | Description |
 |---|---|---|
 | `OLLAMA_URL` | `http://localhost:11434` | Ollama server URL |
-| `OLLAMA_MODEL` | `qwen2.5:14b` | Model for diagram generation |
 | `OPENAI_BASE_URL` | _(empty)_ | OpenAI-compatible API base (optional) |
 | `OPENAI_API_KEY` | _(empty)_ | API key for OpenAI-compatible API |
-| `WHISPER_MODEL` | `medium` | `tiny` / `base` / `small` / `medium` / `large-v3` |
-| `WHISPER_DEVICE` | `auto` | `auto` / `cpu` / `cuda` |
 | `API_KEY` | _(empty)_ | If set, require `X-Api-Key` header on all requests |
 | `PORT` | `7625` | Server port |
 
diff --git a/voice-to-mermaid/backend/.env.example b/voice-to-mermaid/backend/.env.example
index b30b093..1ac6706 100644
--- a/voice-to-mermaid/backend/.env.example
+++ b/voice-to-mermaid/backend/.env.example
@@ -1,31 +1,19 @@
 # voice-to-mermaid backend — copy to .env and fill in
+#
+# Non-secret settings (model names, Whisper config, prompt path, model filter)
+# are in config.yaml — edit that file instead of adding them here.
 
-# ── LLM backend (pick one) ────────────────────────────────────────────────
+# ── LLM backend URLs (secrets — keep out of config.yaml) ─────────────────
 
 # Option A: Ollama (local, recommended for self-hosting)
 OLLAMA_URL=http://localhost:11434
-OLLAMA_MODEL=qwen2.5:14b
-# Comma-separated model name prefixes shown in the picker (empty = show all)
-OLLAMA_MODEL_FILTER=qwen2.5:,qwen3.5:
 
 # Option B: OpenAI-compatible API (vLLM, OpenAI, Together, etc.)
 # OPENAI_BASE_URL=https://api.openai.com/v1
 # OPENAI_API_KEY=sk-...
-# OPENAI_MODEL=gpt-4o-mini
-
-# ── Whisper (transcription) ───────────────────────────────────────────────
-# Model size: tiny | base | small | medium | large-v3
-# Device:     auto | cpu | cuda
-WHISPER_MODEL=medium
-WHISPER_DEVICE=auto
 
 # ── Server ────────────────────────────────────────────────────────────────
 PORT=7625
 # Shared secret — Next.js proxy sends this as X-Api-Key header.
 # Leave blank to disable auth (dev only).
 API_KEY=
-
-# ── Prompts ───────────────────────────────────────────────────────────────
-# Path to mermaid prompt template (relative to this file).
-# Edit prompts/mermaid.txt to customise diagram generation behaviour.
-MERMAID_PROMPT_PATH=prompts/mermaid.txt
diff --git a/voice-to-mermaid/backend/config.yaml b/voice-to-mermaid/backend/config.yaml
index 5f40488..9acf4ae 100644
--- a/voice-to-mermaid/backend/config.yaml
+++ b/voice-to-mermaid/backend/config.yaml
@@ -18,7 +18,11 @@ openai:
   model: "gpt-4o-mini"
 
 whisper:
-  enabled: false   # set true only when requirements.stt.txt deps are installed
+  # true = attempt to load WhisperLiveKit at startup.
+  # If import fails (deps not installed), _stt_available stays False and
+  # /v1/config returns stt_enabled: false — no crash.
+  # Install requirements.stt.txt (or add it to Dockerfile) before setting true.
+  enabled: true
   model: "medium.en"
   language: "en"
   device: "auto"   # "auto", "cuda", "cpu" — maps to WhisperLiveKitConfig backend
diff --git a/voice-to-mermaid/backend/main.py b/voice-to-mermaid/backend/main.py
index 8442ff2..dedfa34 100644
--- a/voice-to-mermaid/backend/main.py
+++ b/voice-to-mermaid/backend/main.py
@@ -71,21 +71,41 @@ def _load_config() -> dict:
 
 _cfg = _load_config()
 
+
+
+def _config_section(name: str) -> dict:
+    section = _cfg.get(name, {})
+    if isinstance(section, dict):
+        return section
+    log.warning("config.%s is not a mapping — using defaults for that section", name)
+    return {}
+
+
+_ollama_cfg = _config_section("ollama")
+_openai_cfg = _config_section("openai")
+_whisper_cfg = _config_section("whisper")
+_paths_cfg = _config_section("paths")
+
+
 # Secrets — env only
 OLLAMA_URL = os.environ.get("OLLAMA_URL", "http://localhost:11434").rstrip("/")
 OPENAI_URL = os.environ.get("OPENAI_BASE_URL", "").rstrip("/")
 OPENAI_KEY = os.environ.get("OPENAI_API_KEY", "")
 
 # Settings — config.yaml only; edit config.yaml to change these
-OLLAMA_MODEL = _cfg.get("ollama", {}).get("default_model", "qwen3:8b")
-OPENAI_MODEL = _cfg.get("openai", {}).get("model", "gpt-4o-mini")
-WHISPER_ENABLED = _cfg.get("whisper", {}).get("enabled", False)
-WHISPER_MODEL = _cfg.get("whisper", {}).get("model", "medium.en")
-WHISPER_LANG = _cfg.get("whisper", {}).get("language", "en")
-WHISPER_DEVICE = _cfg.get("whisper", {}).get("device", "auto")
-PROMPT_PATH = Path(_cfg.get("paths", {}).get("prompt", "prompts/mermaid.txt"))
-LOG_DIR = Path(_cfg.get("paths", {}).get("log_dir", "data/logs"))
-_MODEL_FILTER: list[str] = [str(p) for p in (_cfg.get("ollama", {}).get("model_filter") or [])]
+OLLAMA_MODEL = _ollama_cfg.get("default_model", "qwen3:8b")
+OPENAI_MODEL = _openai_cfg.get("model", "gpt-4o-mini")
+WHISPER_ENABLED = _whisper_cfg.get("enabled", False)
+WHISPER_MODEL = _whisper_cfg.get("model", "medium.en")
+WHISPER_LANG = _whisper_cfg.get("language", "en")
+WHISPER_DEVICE = _whisper_cfg.get("device", "auto")
+PROMPT_PATH = Path(_paths_cfg.get("prompt", "prompts/mermaid.txt"))
+LOG_DIR = Path(_paths_cfg.get("log_dir", "data/logs"))
+_MODEL_FILTER: list[str] = [str(p) for p in (_ollama_cfg.get("model_filter") or [])]
+
+# Set True only after WhisperLiveKit loads successfully at startup.
+# WHISPER_ENABLED=True but import fails → _stt_available stays False.
+_stt_available: bool = False
 
 _ollama_models_cache: list[dict] | None = None
 
@@ -253,7 +273,7 @@ async def _to_mermaid(
 
 @asynccontextmanager
 async def _lifespan(app: FastAPI):
-    global _transcription_engine
+    global _transcription_engine, _stt_available
     _init_log_file()
     if WHISPER_ENABLED:
         try:
@@ -279,6 +299,7 @@ async def _lifespan(app: FastAPI):
                 pcm_input=False,
             )
         )
+        _stt_available = True
         log.info("WhisperLiveKit ready")
     else:
         log.info("STT disabled (whisper.enabled=false) — audio transcription unavailable")
@@ -319,8 +340,8 @@ async def config():
         "ollama_model": OLLAMA_MODEL,
         "ollama_models": _ollama_models_cache,
         "openai_model": OPENAI_MODEL,
-        "stt_enabled": WHISPER_ENABLED,
-        "whisper_model": WHISPER_MODEL if WHISPER_ENABLED else None,
+        "stt_enabled": _stt_available,
+        "whisper_model": WHISPER_MODEL if _stt_available else None,
     }