Klayout

CI Docs

Read-only MCP server for KLayout. It opens GDS/OAS layouts, inspects geometry and hierarchy, renders deterministic PNGs, and runs batch DRC with structured JSON output.

Install

Fastest one-off run:

uvx klayout-mcp@latest

Install once:

uv tool install klayout-mcp

Traditional Python install:

python -m pip install klayout-mcp

For batch DRC, the klayout executable must be on PATH or exposed through KLAYOUT_BIN.

export KLAYOUT_BIN=/Applications/klayout.app/Contents/MacOS/klayout

Quick Start

klayout-mcp is a stdio MCP server. The default launch shape is:

command: uvx
args:    klayout-mcp@latest

If your client cannot use uvx, install the tool once and launch klayout-mcp directly.

Typical workflow:

1. open_layout
2. list_layers
3. list_cells or describe_cell
4. query_region
5. measure_geometry
6. analyze_waveguide
7. render_view
8. run_drc_script
9. extract_markers
10. close_session

Client Setup

More copy-paste examples live in examples/mcp/README.md.

Codex

[mcp_servers.klayout]
command = "uvx"
args = ["klayout-mcp@latest"]

[mcp_servers.klayout.env]
KLAYOUT_BIN = "/Applications/klayout.app/Contents/MacOS/klayout"

Or add it with the CLI:

codex mcp add klayout \
  --env KLAYOUT_BIN=/Applications/klayout.app/Contents/MacOS/klayout \
  -- uvx klayout-mcp@latest

Claude Code

{
  "mcpServers": {
    "klayout": {
      "command": "uvx",
      "args": ["klayout-mcp@latest"],
      "env": {
        "KLAYOUT_BIN": "/Applications/klayout.app/Contents/MacOS/klayout"
      }
    }
  }
}

Or add it with the CLI:

claude mcp add --transport stdio klayout \
  --scope project \
  --env KLAYOUT_BIN=/Applications/klayout.app/Contents/MacOS/klayout \
  -- uvx klayout-mcp@latest

Cursor

Cursor is file-config based:

{
  "mcpServers": {
    "klayout": {
      "command": "uvx",
      "args": ["klayout-mcp@latest"],
      "env": {
        "KLAYOUT_BIN": "/Applications/klayout.app/Contents/MacOS/klayout"
      }
    }
  }
}

OpenCode

OpenCode is file-config based:

{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "klayout": {
      "type": "local",
      "command": ["uvx", "klayout-mcp@latest"],
      "enabled": true,
      "environment": {
        "KLAYOUT_BIN": "/Applications/klayout.app/Contents/MacOS/klayout"
      }
    }
  }
}

Other MCP Hosts

Use:

• command: uvx
• args: ["klayout-mcp@latest"]
• env: KLAYOUT_BIN when needed

Tools

• Session: open_layout, close_session
• Structure: list_layers, list_cells, describe_cell
• Geometry: query_region, measure_geometry, analyze_waveguide
• View: set_view, render_view
• DRC: run_drc_script, extract_markers

Configuration

Variable	Purpose	Default
KLAYOUT_MCP_ARTIFACT_ROOT	Root directory for runtime artifacts	<repo>/.artifacts
KLAYOUT_MCP_SESSION_TTL_SECONDS	Session inactivity timeout	3600
KLAYOUT_BIN	KLayout batch executable for DRC	klayout

Behavior:

• any absolute local path can be used for layouts and DRC scripts
• artifact paths returned by tools are absolute
• sessions expire lazily after inactivity
• close_session removes the session artifact directory

Artifacts And Errors

Artifacts are stored under .artifacts/sessions/<session_id>/ and include renders, DRC reports, marker crops, and logs.

Tool failures return structured JSON such as:

{
  "code": "FILE_NOT_FOUND",
  "message": "Layout file does not exist",
  "details": {
    "path": "/abs/path/to/missing.gds"
  }
}

Common codes: FILE_NOT_FOUND, SESSION_NOT_FOUND, INVALID_BOX, INVALID_LAYER, INVALID_TARGET, DRC_RUN_FAILED.

Development

For a source checkout:

uv sync --extra dev
uv run klayout-mcp

If an MCP client needs to launch the checkout directly:

command: uv
args:    --directory /abs/path/to/klayout-mcp run klayout-mcp

Contributor workflow is in CONTRIBUTING.md. Release notes are in CHANGELOG.md.

Releases

Normal releases are automated with release-please.

• merge Conventional Commits to main
• release-please opens or updates a release PR
• merging that release PR updates pyproject.toml, CHANGELOG.md, creates the tag and GitHub release, and publishes to PyPI

To let the release PR run normal CI under branch protection, configure a repository secret named RELEASE_PLEASE_TOKEN with a GitHub token that can open pull requests. Without it, release-please falls back to github.token, which may not trigger PR workflows.

The manual release.yml workflow remains available for TestPyPI validation and recovery publishing.

Reference

• docs/specs/2026-03-05-klayout-observer-mcp-contract.md
• docs/plans/2026-03-05-klayout-observer-mcp-design.md
• docs/plans/2026-03-05-klayout-observer-mcp-implementation-plan.md

Documentation Site

The repository is configured for Read the Docs with MkDocs.

Build the docs locally:

uv run --extra docs mkdocs build --strict

Serve the docs locally:

uv run --extra docs mkdocs serve

After importing the GitHub repository into Read the Docs, it can build directly from the default branch using .readthedocs.yaml.