diff --git a/tests/tools/test_transcription_tools.py b/tests/tools/test_transcription_tools.py
new file mode 100644
index 00000000..6750f28d
--- /dev/null
+++ b/tests/tools/test_transcription_tools.py
@@ -0,0 +1,199 @@
+"""Tests for tools.transcription_tools -- provider resolution and model correction."""
+
+import os
+import struct
+import wave
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+
+# ============================================================================
+# Fixtures
+# ============================================================================
+
+@pytest.fixture
+def sample_wav(tmp_path):
+    """Create a minimal valid WAV file (1 second of silence at 16kHz)."""
+    wav_path = tmp_path / "test.wav"
+    n_frames = 16000
+    silence = struct.pack(f"<{n_frames}h", *([0] * n_frames))
+
+    with wave.open(str(wav_path), "wb") as wf:
+        wf.setnchannels(1)
+        wf.setsampwidth(2)
+        wf.setframerate(16000)
+        wf.writeframes(silence)
+
+    return str(wav_path)
+
+
+@pytest.fixture(autouse=True)
+def clean_env(monkeypatch):
+    """Ensure no real API keys leak into tests."""
+    monkeypatch.delenv("VOICE_TOOLS_OPENAI_KEY", raising=False)
+    monkeypatch.delenv("GROQ_API_KEY", raising=False)
+
+
+# ============================================================================
+# _resolve_stt_provider
+# ============================================================================
+
+class TestResolveSTTProvider:
+    def test_openai_preferred_over_groq(self, monkeypatch):
+        monkeypatch.setenv("VOICE_TOOLS_OPENAI_KEY", "sk-test")
+        monkeypatch.setenv("GROQ_API_KEY", "gsk-test")
+
+        from tools.transcription_tools import _resolve_stt_provider
+        key, url, provider = _resolve_stt_provider()
+
+        assert provider == "openai"
+        assert key == "sk-test"
+        assert "openai.com" in url
+
+    def test_groq_fallback(self, monkeypatch):
+        monkeypatch.setenv("GROQ_API_KEY", "gsk-test")
+
+        from tools.transcription_tools import _resolve_stt_provider
+        key, url, provider = _resolve_stt_provider()
+
+        assert provider == "groq"
+        assert key == "gsk-test"
+        assert "groq.com" in url
+
+    def test_no_keys_returns_none(self):
+        from tools.transcription_tools import _resolve_stt_provider
+        key, url, provider = _resolve_stt_provider()
+
+        assert provider == "none"
+        assert key is None
+        assert url is None
+
+
+# ============================================================================
+# transcribe_audio -- no API key
+# ============================================================================
+
+class TestTranscribeAudioNoKey:
+    def test_returns_error_when_no_key(self):
+        from tools.transcription_tools import transcribe_audio
+        result = transcribe_audio("/tmp/test.wav")
+
+        assert result["success"] is False
+        assert "No STT API key" in result["error"]
+
+    def test_returns_error_for_missing_file(self, monkeypatch):
+        monkeypatch.setenv("GROQ_API_KEY", "gsk-test")
+
+        from tools.transcription_tools import transcribe_audio
+        result = transcribe_audio("/nonexistent/audio.wav")
+
+        assert result["success"] is False
+        assert "not found" in result["error"]
+
+
+# ============================================================================
+# Model auto-correction
+# ============================================================================
+
+class TestModelAutoCorrection:
+    def test_groq_corrects_openai_model(self, monkeypatch, sample_wav):
+        monkeypatch.setenv("GROQ_API_KEY", "gsk-test")
+
+        mock_client = MagicMock()
+        mock_client.audio.transcriptions.create.return_value = "hello world"
+
+        with patch("openai.OpenAI", return_value=mock_client):
+            from tools.transcription_tools import transcribe_audio, DEFAULT_GROQ_STT_MODEL
+            result = transcribe_audio(sample_wav, model="whisper-1")
+
+        assert result["success"] is True
+        assert result["transcript"] == "hello world"
+        # Verify the model was corrected to Groq default
+        call_kwargs = mock_client.audio.transcriptions.create.call_args
+        assert call_kwargs.kwargs["model"] == DEFAULT_GROQ_STT_MODEL
+
+    def test_openai_corrects_groq_model(self, monkeypatch, sample_wav):
+        monkeypatch.setenv("VOICE_TOOLS_OPENAI_KEY", "sk-test")
+
+        mock_client = MagicMock()
+        mock_client.audio.transcriptions.create.return_value = "hello world"
+
+        with patch("openai.OpenAI", return_value=mock_client):
+            from tools.transcription_tools import transcribe_audio, DEFAULT_STT_MODEL
+            result = transcribe_audio(sample_wav, model="whisper-large-v3-turbo")
+
+        assert result["success"] is True
+        call_kwargs = mock_client.audio.transcriptions.create.call_args
+        assert call_kwargs.kwargs["model"] == DEFAULT_STT_MODEL
+
+    def test_none_model_uses_provider_default(self, monkeypatch, sample_wav):
+        monkeypatch.setenv("GROQ_API_KEY", "gsk-test")
+
+        mock_client = MagicMock()
+        mock_client.audio.transcriptions.create.return_value = "test"
+
+        with patch("openai.OpenAI", return_value=mock_client):
+            from tools.transcription_tools import transcribe_audio, DEFAULT_GROQ_STT_MODEL
+            transcribe_audio(sample_wav, model=None)
+
+        call_kwargs = mock_client.audio.transcriptions.create.call_args
+        assert call_kwargs.kwargs["model"] == DEFAULT_GROQ_STT_MODEL
+
+    def test_compatible_model_not_overridden(self, monkeypatch, sample_wav):
+        monkeypatch.setenv("GROQ_API_KEY", "gsk-test")
+
+        mock_client = MagicMock()
+        mock_client.audio.transcriptions.create.return_value = "test"
+
+        with patch("openai.OpenAI", return_value=mock_client):
+            from tools.transcription_tools import transcribe_audio
+            transcribe_audio(sample_wav, model="whisper-large-v3")
+
+        call_kwargs = mock_client.audio.transcriptions.create.call_args
+        assert call_kwargs.kwargs["model"] == "whisper-large-v3"
+
+
+# ============================================================================
+# transcribe_audio -- success path
+# ============================================================================
+
+class TestTranscribeAudioSuccess:
+    def test_successful_transcription(self, monkeypatch, sample_wav):
+        monkeypatch.setenv("GROQ_API_KEY", "gsk-test")
+
+        mock_client = MagicMock()
+        mock_client.audio.transcriptions.create.return_value = "hello world"
+
+        with patch("openai.OpenAI", return_value=mock_client):
+            from tools.transcription_tools import transcribe_audio
+            result = transcribe_audio(sample_wav)
+
+        assert result["success"] is True
+        assert result["transcript"] == "hello world"
+        assert result["provider"] == "groq"
+
+    def test_api_error_returns_failure(self, monkeypatch, sample_wav):
+        monkeypatch.setenv("GROQ_API_KEY", "gsk-test")
+
+        mock_client = MagicMock()
+        mock_client.audio.transcriptions.create.side_effect = Exception("API error")
+
+        with patch("openai.OpenAI", return_value=mock_client):
+            from tools.transcription_tools import transcribe_audio
+            result = transcribe_audio(sample_wav)
+
+        assert result["success"] is False
+        assert "API error" in result["error"]
+
+    def test_whitespace_transcript_stripped(self, monkeypatch, sample_wav):
+        monkeypatch.setenv("VOICE_TOOLS_OPENAI_KEY", "sk-test")
+
+        mock_client = MagicMock()
+        mock_client.audio.transcriptions.create.return_value = "  hello world  \n"
+
+        with patch("openai.OpenAI", return_value=mock_client):
+            from tools.transcription_tools import transcribe_audio
+            result = transcribe_audio(sample_wav)
+
+        assert result["transcript"] == "hello world"