tidy3d-mcp 0.13.3

Local stdio FastMCP server for Tidy3D

Tidy3D MCP

A local Model Context Protocol (MCP) server that lets clients drive the Flexcompute Tidy3D viewer and consume viewer artifacts without needing a browser session.

Capabilities

• Authenticates against the remote FlexAgent MCP endpoint using your Tidy3D API key.
• Proxies viewer automation commands such as launching the viewer, rotating the camera, toggling structure visibility, running simulation health checks, and capturing screenshots.
• Returns viewer captures as MCP images so downstream tools can consume them immediately.

Requirements

• Python 3.10 or newer
• uv for dependency management
• Network access to the target FlexAgent MCP deployment (defaults to the hosted https://flexagent.dev-simulation.cloud/ endpoint)

Installation

uv sync

This resolves the project environment and installs the tidy3d-mcp console entry point.

Usage

Start the server from the project root and supply your API key (see Tidy3D installation docs for instructions to obtain it):

uv run tidy3d-mcp -- --api-key YOUR_TIDY3D_API_KEY

The server listens on stdio for MCP requests and forwards them to the remote FlexAgent server using the provided API key for authentication.

Enabling Viewer Automation

Viewer-facing tools are opt-in. Launch the proxy with --enable-viewer to activate them. Pair the flag with --host vscode (default) or --host cursor, depending on which desktop is available to handle the deeplink. When the flag is present the server:

1. Chooses a free localhost port.
2. Opens a vscode://Flexcompute.tidy3d/bridge?... or cursor://Flexcompute.tidy3d/bridge?... URI so the desktop extension can own the bridge on that port and expose the HTTP endpoint.
3. Waits (15s max) for the extension to acknowledge the port by standing up the /viewer/* bridge.

If the deeplink cannot be handled or the bridge never binds, viewer tools are skipped and the proxy continues as a simple API gateway.

Integrating with MCP Hosts

• VS Code / Cursor: Select the "Tidy3D MCP" binary (uv run tidy3d-mcp) when configuring an stdio MCP provider.
• Custom hosts: Launch the command above and connect using the Model Context Protocol over the process stdio pipes.

Configuration

Environment variables control the server at startup:

Variable	Purpose	Default
REMOTE_MCP_URL	Target MCP endpoint to proxy.	https://flexagent.dev-simulation.cloud/

Pass --api-key whenever you launch the server. Viewer tooling is available only when --enable-viewer is provided and the Tidy3D extension accepts the bridge deeplink. Hosts that wrap the binary must forward both arguments when spawning the process.

Tools Exposed to Clients

Tool	Availability	Description
validate_simulation	Requires --enable-viewer	Launches or re-checks a simulation, returning the viewer_id, diagnostic status, warnings, and the evaluated code slice.
rotate_viewer	Requires --enable-viewer	Rotates the active viewer toward the requested direction (e.g. TOP, BOTTOM).
show_structures	Requires --enable-viewer	Applies a boolean visibility array to the current viewer structures.
capture	Requires --enable-viewer	Captures the current frame of the viewer.

Development Tips

• Run uv run ruff check to lint the project and uv run ruff format to apply formatting.
• The server relies on fastmcp.as_proxy; consult the upstream FastMCP documentation for advanced configuration such as custom authentication flows or additional transports.
• When debugging viewer interactions, inspect the returned data_url to confirm that capture payloads reach the client.

Troubleshooting

• API key rejected: Confirm the key is current by visiting the Tidy3D account page and copying a fresh key. Keys can be regenerated through the web interface if needed.
• Viewer fails to start: Verify the simulation file exists, the MCP host provides the correct working directory, and the remote FlexAgent endpoint is reachable.