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Install Cities2 MCP and Modding Toolkit

Choose your client: Claude Code | Claude desktop | Codex CLI | Codex app | Google Antigravity

Marketplace installs include the bundled wiki corpus, the optional local game encyclopedia lookup, five agent skills, and the plugin-local MCP server launcher. Use the direct MCP command only when a client cannot install plugins or when you want to pin the Python package directly.

Claude

Install in Claude Code

Run these inside Claude Code:

/plugin marketplace add mayor-modder/Mayor-Modder-Cities2-Plugins

/plugin install cities2-mcp@cities2-mcp

Start a new Claude Code session in your mod project folder. The plugin starts cities2-mcp there so workflow tools can scaffold, read, write, build, and package files.

Install in Claude desktop

  1. Open either the Cowork or Code tab.
  2. Select Customize in the sidebar.
  3. Next to Personal plugins, click +.
  4. Choose Create Plugin > Add marketplace.
  5. Enter mayor-modder/Mayor-Modder-Cities2-Plugins.
  6. Install and enable Cities2 MCP and Modding Toolkit.

Using skills in Claude

/cities2-knowledge Why is my office demand stuck near zero?

/cities2-modding Scaffold a small Cities: Skylines II UI mod in this project folder, then build it.

/cities2-mod-review Review this Cities: Skylines II mod before I install it.

Codex

Install in Codex CLI

In your system terminal, add this repository as a Codex plugin marketplace:

codex plugin marketplace add mayor-modder/Mayor-Modder-Cities2-Plugins

Then start Codex from your project folder:

codex

Enter /plugin, install Cities2 MCP and Modding Toolkit, then restart Codex in the same folder.

Install in the Codex app

  1. Open the Codex app and choose Plugins from the sidebar.
  2. Click the arrow on the side of the Create button to open the dropdown.
  3. Click Add marketplace.
  4. Enter source mayor-modder/Mayor-Modder-Cities2-Plugins and click Add marketplace.
  5. Install and enable Cities2 MCP and Modding Toolkit.
  6. Fully exit Codex and restart.

Using skills in Codex

$cities2-mcp:cities2-knowledge How can I get more people to use my subway line?

$cities2-mcp:cities2-modding Scaffold a small Cities: Skylines II UI mod in this project folder, then build it.

$cities2-mcp:cities2-mod-review Review this Cities: Skylines II mod before I install it.

You can also check available skills with /skills and type $ to pick one.

Known Codex behavior: plugin-bundled MCP servers currently launch from the installed plugin cache, so direct MCP workflow tools may be allowlist-blocked. The bundled cities2-modding skill handles this by copying the bundled template as an explicit fallback, building with normal Codex workspace access, and stopping after build verification.

Google Antigravity

Install in Google Antigravity

Run this once in PowerShell:

agy plugin install https://github.com/mayor-modder/Cities2-MCP/

Then restart the Google Antigravity app, or open Antigravity CLI with agy from your mod workspace.

Using skills in Google Antigravity

Type /cities2 and choose one of the Cities2 skills.

/cities2-knowledge Why are my commercial companies complaining about not enough customers?

/cities2-modding Scaffold a small Cities: Skylines II UI mod in this project folder, then build it.

/cities2-mod-review Review this Cities: Skylines II mod before I install it.

Workspace access

Game knowledge and encyclopedia lookup work immediately after install. Mod workflow tools need a trusted workspace, and Claude and Codex usually use the project you opened:

  • In Claude Code and Codex CLI, start the client from the mod project folder.
  • If a tool reports Path must stay inside configured workspaces, add the mod project folder or a trusted parent folder and restart the client.
  • In Claude desktop, that setting is called Trusted mod projects folder.

Codex plugin MCP servers may launch from the plugin cache. If a direct workflow tool is allowlist-blocked, invoke cities2-modding; it has a bundled-template fallback.

Builds run project commands through npm, dotnet, and packaging steps; only build projects you trust. The skills should still hand local playtesting back to you before calling a mod ready to share.

Optional build prerequisites

Knowledge, encyclopedia, and scaffold tools do not require the Cities: Skylines II modding toolchain. Builds may need:

  • UI-only mods need Node.js and npm.
  • C# and hybrid mods need the Cities: Skylines II modding toolchain installed from inside the game.
  • C# and hybrid builds also need dotnet on PATH and Microsoft.NETCore.App 6. in dotnet --list-runtimes.

If a build prerequisite is missing, the agent should stop, explain what is missing, and ask whether you want to install it, keep the scaffold, or continue with edits.

Direct MCP command

The plugin marketplace path is recommended. Use a direct MCP command only for a client that cannot install plugins:

{
  "mcpServers": {
    "cities2-mcp": {
      "command": "uvx",
      "args": [
        "cities2-mcp",
        "--workspace",
        "<TRUSTED_MOD_PROJECT_OR_PARENT_FOLDER>"
      ]
    }
  }
}

The package includes wiki data, so --data-dir is not needed. Omit --workspace when you only want wiki and local encyclopedia tools.

To check or pin the package:

uvx cities2-mcp --version
uvx --refresh cities2-mcp --version

Some clients can load local agent skills separately from MCP server settings. For those clients, install the bundled skills with:

uvx cities2-mcp install-agent-assets

For a source checkout, run python -m cities2_mcp.mcp_server --workspace <folder> from the repository root.

Troubleshooting

Symptom Fix
Server does not appear after install Fully quit and restart the client you installed into.
Path must stay inside configured workspaces Add the mod project folder, or a trusted parent folder containing your mods, to the client or plugin workspace setting.
Codex workflow tools are allowlist-blocked Invoke $cities2-mcp:cities2-modding; the skill can use the bundled-template fallback inside the current Codex workspace.
npm.ps1 is blocked on Windows Use npm.cmd install and npm.cmd run build.
C# build says .NET is missing Install the .NET 6 runtime and confirm with dotnet --list-runtimes.
Game encyclopedia unavailable Wiki tools still work. Set CITIES2_GAME_DIR or CITIES2_LOCALE_COK only if the game is installed somewhere unusual.