write_file_content_to_sandbox
Write content to files in a Modal sandbox for prototyping, code generation, and implementing algorithms in isolated cloud environments.
Instructions
Writes content to a file in a Modal sandbox.
This is useful for writing code, text, or any other content to a file in the sandbox.
Parameters:
- sandbox_id: ID of the target sandbox where code will be written
- sandbox_path: Path where the code file should be created/written in the sandbox
- content: Content to write to the file
Returns a SandboxWriteCodeResponse containing:
- success: Boolean indicating if code was written successfully
- message: Descriptive message about the operation
- file_path: Path where code was written in sandbox
This tool is powerful for:
- Rapid prototyping and code generation
- Creating boilerplate code
- Implementing algorithms from descriptions
- Converting pseudocode to actual code
- Generating test cases
- Creating utility functions and helper code
The tool will:
1. Verify the sandbox is running
2. Write content to specified path in sandbox
3. Handle errors and provide detailed feedback
Input Schema
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| sandbox_id | Yes | ||
| sandbox_path | Yes | ||
| content | Yes |
Implementation Reference
- The main asynchronous handler function that implements the tool logic: fetches the sandbox, checks if running, writes content using a helper thread method, logs, and returns a success response.
async def write_file_content_to_sandbox( self, sandbox_id:str, sandbox_path:str, content:str, ) -> SandboxWriteFileResponse: sandbox = await modal.Sandbox.from_id.aio(sandbox_id) sandbox_status = await sandbox.poll.aio() if sandbox_status is not None: raise ToolError(f"Sandbox {sandbox_id} is not running") # Write to sandbox using thread executor await self._write_sandbox_file_in_thread(sandbox, sandbox_path, content, "w") logger.info(f"Content written successfully to {sandbox_path}") return SandboxWriteFileResponse( success=True, message=f"Content written successfully to {sandbox_path}", file_path=sandbox_path, ) - src/mcp4modal_sandbox/backend/mcp_server.py:151-154 (registration)Tool registration in FastMCP, specifying name, description from ToolDescriptions, and binding the handler method.
mcp_app.tool( name="write_file_content_to_sandbox", description=ToolDescriptions.WRITE_FILE_CONTENT_TO_SANDBOX, )(self.write_file_content_to_sandbox) - Pydantic BaseModel defining the output schema/response structure for the tool.
class SandboxWriteFileResponse(BaseModel): success: bool message: str file_path: str - Helper function to synchronously write file content in a thread pool executor to avoid blocking the async event loop; used by the handler.
async def _write_sandbox_file_in_thread(self, modal_sandbox, file_path: str, content, mode: str = 'wb'): def _sync_write(): with modal_sandbox.open(file_path, mode) as f: f.write(content) loop = asyncio.get_event_loop() return await loop.run_in_executor(self.thread_pool_executor, _sync_write)