diff --git a/.github/workflows/main.yaml b/.github/workflows/main.yaml
index 8bb26a7c..39fc1d76 100644
--- a/.github/workflows/main.yaml
+++ b/.github/workflows/main.yaml
@@ -46,6 +46,16 @@ jobs:
           auto-update-conda: true
           conda-solver: libmamba
 
+      - name: Ensure conda 'defaults' channel not present
+        run: |
+          # Only remove the 'defaults' channel if it exists to avoid CondaKeyError
+          if conda config --show channels | grep -q 'defaults'; then
+            conda config --remove channels defaults
+            echo "Removed 'defaults' channel"
+          else
+            echo "'defaults' channel not present, skipping removal"
+          fi
+
       - name: Install dependencies
         run: |
           poetry check
@@ -56,7 +66,7 @@ jobs:
         if: ${{ github.event_name == 'pull_request' }}
         run: |
           pre-commit install
-          pre-commit run --all-file --verbose
+          pre-commit run --all-files --verbose
 
       - name: Build the book
         run: |
@@ -69,4 +79,4 @@ jobs:
         if: ${{ github.event_name == 'push' }}
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
-          publish_dir: ./build
+          publish_dir: ./build
\ No newline at end of file
diff --git a/src/artbox/cli.py b/src/artbox/cli.py
new file mode 100644
index 00000000..b49529ae
--- /dev/null
+++ b/src/artbox/cli.py
@@ -0,0 +1,29 @@
+# ...existing code...
+from artbox.validators import validate_io_paths
+import sys
+# ...existing code...
+
+# INSERT: extract common arg names and validate extensions
+input_path = getattr(args, "input_path", None) or getattr(args, "input", None) or None
+output_path = getattr(args, "output_path", None) or getattr(args, "output", None) or None
+
+operation = None
+for attr in ("operation", "op", "command", "cmd", "subcommand", "mode"):
+    val = getattr(args, attr, None)
+    if isinstance(val, str) and val:
+        operation = val
+        break
+
+if isinstance(operation, str):
+    ol = operation.lower()
+    if ol in ("tts", "text-to-speech", "text->speech"):
+        operation = "text-to-speech"
+    elif ol in ("stt", "speech-to-text", "speech->text"):
+        operation = "speech-to-text"
+
+try:
+    validate_io_paths(input_path, output_path, operation)
+except ValueError as e:
+    print(f"Error: {e}", file=sys.stderr)
+    raise SystemExit(2)
+# ...existing code...
\ No newline at end of file
diff --git a/src/artbox/validators.py b/src/artbox/validators.py
new file mode 100644
index 00000000..07c372cd
--- /dev/null
+++ b/src/artbox/validators.py
@@ -0,0 +1,141 @@
+from pathlib import Path
+from typing import Optional
+
+AUDIO_EXTS = {".mp3", ".wav", ".ogg", ".flac", ".m4a", ".aac"}
+TEXT_EXTS = {".txt", ".md", ".srt", ".vtt", ".json"}
+
+
+def _ext_of(path: Optional[str]) -> str:
+    return Path(path).suffix.lower() if path else ""
+
+
+def validate_io_paths(input_path: Optional[str], output_path: Optional[str], operation: Optional[str] = None) -> None:
+    """
+    Validate input/output extensions for common operations.
+
+    operation can be:
+      - 'text-to-speech' / 'text->speech' / 'tts'
+      - 'speech-to-text' / 'speech->text' / 'stt'
+      - None (best-effort inference)
+
+    Raises ValueError on invalid combinations.
+    """
+    op = (operation or "").lower()
+    in_ext = _ext_of(input_path)
+    out_ext = _ext_of(output_path)
+
+    tts_ops = {"text-to-speech", "text->speech", "tts"}
+    stt_ops = {"speech-to-text", "speech->text", "stt"}
+
+    if op in tts_ops:
+        if not output_path or out_ext == "":
+            raise ValueError("text->speech requires an audio output file (e.g. --output-path out.mp3).")
+        if out_ext not in AUDIO_EXTS:
+            raise ValueError(f"Invalid output audio format '{out_ext}'. Supported: {', '.join(sorted(AUDIO_EXTS))}")
+
+    elif op in stt_ops:
+        if not input_path or in_ext == "" or in_ext not in AUDIO_EXTS:
+            raise ValueError(f"speech->text requires an audio input file (supported: {', '.join(sorted(AUDIO_EXTS))}).")
+        if not output_path or out_ext == "" or out_ext not in TEXT_EXTS:
+            raise ValueError(f"speech->text requires a text output file (supported: {', '.join(sorted(TEXT_EXTS))}).")
+
+    else:
+        # Infer operation by extensions and validate.
+        inferred_op = None
+        if in_ext:
+            if in_ext in AUDIO_EXTS:
+                inferred_op = "speech-to-text"
+            elif in_ext in TEXT_EXTS:
+                inferred_op = "text-to-speech"
+        if not inferred_op and out_ext:
+            if out_ext in AUDIO_EXTS:
+                inferred_op = "text-to-speech"
+            elif out_ext in TEXT_EXTS:
+                inferred_op = "speech-to-text"
+
+        if inferred_op == "text-to-speech":
+            if not output_path or out_ext == "":
+                raise ValueError("text->speech requires an audio output file (e.g. --output-path out.mp3).")
+            if out_ext not in AUDIO_EXTS:
+                raise ValueError(f"Invalid output audio format '{out_ext}'. Supported: {', '.join(sorted(AUDIO_EXTS))}")
+        elif inferred_op == "speech-to-text":
+            if not input_path or in_ext == "" or in_ext not in AUDIO_EXTS:
+                raise ValueError(f"speech->text requires an audio input file (supported: {', '.join(sorted(AUDIO_EXTS))}).")
+            if not output_path or out_ext == "" or out_ext not in TEXT_EXTS:
+                raise ValueError(f"speech->text requires a text output file (supported: {', '.join(sorted(TEXT_EXTS))}).")
+        else:
+            if input_path and in_ext and in_ext not in AUDIO_EXTS.union(TEXT_EXTS):
+                raise ValueError(f"Unsupported input extension '{in_ext}'. Supported: audio {', '.join(sorted(AUDIO_EXTS))} or text {', '.join(sorted(TEXT_EXTS))}.")
+            if output_path and out_ext and out_ext not in AUDIO_EXTS.union(TEXT_EXTS):
+                raise ValueError(f"Unsupported output extension '{out_ext}'. Supported: audio {', '.join(sorted(AUDIO_EXTS))} or text {', '.join(sorted(TEXT_EXTS))}.")
+
+from pathlib import Path
+from typing import Optional
+
+AUDIO_EXTS = {".mp3", ".wav", ".ogg", ".flac", ".m4a", ".aac"}
+TEXT_EXTS = {".txt", ".md", ".srt", ".vtt", ".json"}
+
+
+def _ext_of(path: Optional[str]) -> str:
+    return Path(path).suffix.lower() if path else ""
+
+
+def validate_io_paths(input_path: Optional[str], output_path: Optional[str], operation: Optional[str] = None) -> None:
+    """
+    Validate input/output extensions for common operations.
+
+    operation can be:
+      - 'text-to-speech' / 'text->speech' / 'tts'
+      - 'speech-to-text' / 'speech->text' / 'stt'
+      - None (best-effort inference)
+
+    Raises ValueError on invalid combinations.
+    """
+    op = (operation or "").lower()
+    in_ext = _ext_of(input_path)
+    out_ext = _ext_of(output_path)
+
+    tts_ops = {"text-to-speech", "text->speech", "tts"}
+    stt_ops = {"speech-to-text", "speech->text", "stt"}
+
+    if op in tts_ops:
+        if not output_path or out_ext == "":
+            raise ValueError("text->speech requires an audio output file (e.g. --output-path out.mp3).")
+        if out_ext not in AUDIO_EXTS:
+            raise ValueError(f"Invalid output audio format '{out_ext}'. Supported: {', '.join(sorted(AUDIO_EXTS))}")
+
+    elif op in stt_ops:
+        if not input_path or in_ext == "" or in_ext not in AUDIO_EXTS:
+            raise ValueError(f"speech->text requires an audio input file (supported: {', '.join(sorted(AUDIO_EXTS))}).")
+        if not output_path or out_ext == "" or out_ext not in TEXT_EXTS:
+            raise ValueError(f"speech->text requires a text output file (supported: {', '.join(sorted(TEXT_EXTS))}).")
+
+    else:
+        # Infer operation by extensions and validate.
+        inferred_op = None
+        if in_ext:
+            if in_ext in AUDIO_EXTS:
+                inferred_op = "speech-to-text"
+            elif in_ext in TEXT_EXTS:
+                inferred_op = "text-to-speech"
+        if not inferred_op and out_ext:
+            if out_ext in AUDIO_EXTS:
+                inferred_op = "text-to-speech"
+            elif out_ext in TEXT_EXTS:
+                inferred_op = "speech-to-text"
+
+        if inferred_op == "text-to-speech":
+            if not output_path or out_ext == "":
+                raise ValueError("text->speech requires an audio output file (e.g. --output-path out.mp3).")
+            if out_ext not in AUDIO_EXTS:
+                raise ValueError(f"Invalid output audio format '{out_ext}'. Supported: {', '.join(sorted(AUDIO_EXTS))}")
+        elif inferred_op == "speech-to-text":
+            if not input_path or in_ext == "" or in_ext not in AUDIO_EXTS:
+                raise ValueError(f"speech->text requires an audio input file (supported: {', '.join(sorted(AUDIO_EXTS))}).")
+            if not output_path or out_ext == "" or out_ext not in TEXT_EXTS:
+                raise ValueError(f"speech->text requires a text output file (supported: {', '.join(sorted(TEXT_EXTS))}).")
+        else:
+            if input_path and in_ext and in_ext not in AUDIO_EXTS.union(TEXT_EXTS):
+                raise ValueError(f"Unsupported input extension '{in_ext}'. Supported: audio {', '.join(sorted(AUDIO_EXTS))} or text {', '.join(sorted(TEXT_EXTS))}.")
+            if output_path and out_ext and out_ext not in AUDIO_EXTS.union(TEXT_EXTS):
+                raise ValueError(f"Unsupported output extension '{out_ext}'. Supported: audio {', '.join(sorted(AUDIO_EXTS))} or text {', '.join(sorted(TEXT_EXTS))}.")
\ No newline at end of file