Add DEFAULT_SYSTEM_PROMPT configuration for Google Gemini pipeline

Co-authored-by: owndev <69784886+owndev@users.noreply.github.com>

Author: Copilot

docs/google-gemini-integration.md

@@ -80,6 +80,12 @@ GOOGLE_MODEL_CACHE_TTL=600
 # Default: 2
 GOOGLE_RETRY_COUNT=2
 
+# Default system prompt applied to all chats
+# If a user-defined system prompt exists, this is prepended to it
+# Leave empty to disable
+# Default: "" (empty, disabled)
+GOOGLE_DEFAULT_SYSTEM_PROMPT=""
+
 # Image processing optimization settings
 # Maximum image size in MB before compression is applied
 # Default: 15.0
@@ -245,6 +251,47 @@ To use this filter, ensure it's enabled in your Open WebUI configuration. Then,
 
 Native tool calling is enabled/disabled via the standard 'Function calling' Open Web UI toggle.
 
+## Default System Prompt
+
+The Google Gemini pipeline supports a configurable default system prompt that is applied to all chats. This is useful when you want to consistently apply certain behaviors or instructions to all Gemini models without having to configure each model individually.
+
+### How It Works
+
+- **Default Only**: If only `GOOGLE_DEFAULT_SYSTEM_PROMPT` is set and no user-defined system prompt exists, the default prompt is used as the system instruction.
+- **User Only**: If only a user-defined system prompt exists (from model settings), it is used as-is.
+- **Both**: If both are set, the default system prompt is **prepended** to the user-defined prompt, separated by a blank line. This allows you to have base instructions that apply to all chats while still allowing model-specific customization.
+
+### Configuration
+
+Set via environment variable:
+
+```bash
+# Default system prompt applied to all chats
+# If a user-defined system prompt exists, this is prepended to it
+GOOGLE_DEFAULT_SYSTEM_PROMPT="You are a helpful AI assistant. Always be concise and accurate."
+```
+
+Or configure through the pipeline valves in Open WebUI's Admin panel.
+
+### Example
+
+If your default system prompt is:
+```
+You are a helpful AI assistant.
+```
+
+And your model-specific system prompt is:
+```
+Always respond in formal English.
+```
+
+The combined system prompt sent to Gemini will be:
+```
+You are a helpful AI assistant.
+
+Always respond in formal English.
+```
+
 ## Thinking Configuration
 
 The Google Gemini pipeline supports advanced thinking configuration to control how much reasoning and computation is applied by the model.

pipelines/google/google_gemini.py

@@ -206,6 +206,11 @@ class Valves(BaseModel):
             default=int(os.getenv("GOOGLE_RETRY_COUNT", "2")),
             description="Number of times to retry API calls on temporary failures",
         )
+        DEFAULT_SYSTEM_PROMPT: str = Field(
+            default=os.getenv("GOOGLE_DEFAULT_SYSTEM_PROMPT", ""),
+            description="Default system prompt applied to all chats. If a user-defined system prompt exists, "
+            "this is prepended to it. Leave empty to disable.",
+        )
 
         # Image Processing Configuration
         IMAGE_MAX_SIZE_MB: float = Field(
@@ -284,6 +289,39 @@ def _deduplicate_images(self, images: List[Dict[str, Any]]) -> List[Dict[str, An
             result.append(part)
         return result
 
+    def _combine_system_prompts(
+        self, user_system_prompt: Optional[str]
+    ) -> Optional[str]:
+        """Combine default system prompt with user-defined system prompt.
+
+        If DEFAULT_SYSTEM_PROMPT is set and user_system_prompt exists,
+        the default is prepended to the user's prompt.
+        If only DEFAULT_SYSTEM_PROMPT is set, it is used as the system prompt.
+        If only user_system_prompt is set, it is used as-is.
+
+        Args:
+            user_system_prompt: The user-defined system prompt from messages (may be None)
+
+        Returns:
+            Combined system prompt or None if neither is set
+        """
+        default_prompt = self.valves.DEFAULT_SYSTEM_PROMPT.strip()
+        user_prompt = user_system_prompt.strip() if user_system_prompt else ""
+
+        if default_prompt and user_prompt:
+            combined = f"{default_prompt}\n\n{user_prompt}"
+            self.log.debug(
+                f"Combined system prompts: default ({len(default_prompt)} chars) + "
+                f"user ({len(user_prompt)} chars) = {len(combined)} chars"
+            )
+            return combined
+        elif default_prompt:
+            self.log.debug(f"Using default system prompt ({len(default_prompt)} chars)")
+            return default_prompt
+        elif user_prompt:
+            return user_prompt
+        return None
+
     def _apply_order_and_limit(
         self,
         history: List[Dict[str, Any]],
@@ -374,12 +412,15 @@ async def _build_image_generation_contents(
 
         Returns tuple (contents, system_instruction) where system_instruction is extracted from system messages.
         """
-        # Extract system instruction first
-        system_instruction = next(
+        # Extract user-defined system instruction first
+        user_system_instruction = next(
             (msg["content"] for msg in messages if msg.get("role") == "system"),
             None,
         )
 
+        # Combine with default system prompt if configured
+        system_instruction = self._combine_system_prompts(user_system_instruction)
+
         last_user_msg = next(
             (m for m in reversed(messages) if m.get("role") == "user"), None
         )
@@ -848,12 +889,15 @@ def _prepare_content(
         Returns:
             Tuple of (prepared content list, system message string or None)
         """
-        # Extract system message
-        system_message = next(
+        # Extract user-defined system message
+        user_system_message = next(
             (msg["content"] for msg in messages if msg.get("role") == "system"),
             None,
         )
 
+        # Combine with default system prompt if configured
+        system_message = self._combine_system_prompts(user_system_message)
+
         # Prepare contents for the API
         contents = []
         for message in messages:
@@ -2074,7 +2118,7 @@ async def pipe(
                     # For image generation, system_instruction is integrated into the prompt
                     # so it will be None here (this is expected and correct)
                     self.log.debug(
-                        f"Image generation mode: system instruction integrated into prompt"
+                        "Image generation mode: system instruction integrated into prompt"
                     )
                 except ValueError as ve:
                     return f"Error: {ve}"