test-marketplace

test-plugin

A minimal Claude Code marketplace plugin for testing installation flows.

Installation

/plugin marketplace add seanlynch-fivetran/test-plugin
/plugin install test-plugin@test-marketplace

Structure

Everything lives under .marketplace/test-plugin/ — no build step, no source directories. Dual metadata: .claude-plugin/ for Claude Code, .codex-plugin/ for Codex.

Claude Code

Marketplace defined at repo root in .claude-plugin/marketplace.json. Plugin contents under .marketplace/test-plugin/ with:

• .claude-plugin/plugin.json — name, version, author, userConfig
• .mcp.json — MCP server definitions (separate file; can also be inline in plugin.json)
• skills/test-skill/SKILL.md — skill definition with YAML frontmatter
• mcps/test/server.py — the actual MCP server

Key vars: ${CLAUDE_PLUGIN_ROOT}, ${CLAUDE_PLUGIN_DATA}, ${user_config.*}

Codex

No repo-root marketplace file needed here — the consuming repo defines .agents/plugins/marketplace.json pointing at the plugin directory.

Plugin uses .codex-plugin/plugin.json instead, which adds:

• interface object — displayName, shortDescription, developerName, category, capabilities, defaultPrompt, brandColor, etc.
• mcpServers — path reference to .mcp.json (not inline)
• skills — path reference to skills directory

Marketplace entries include policy.installation (AVAILABLE, INSTALLED_BY_DEFAULT, NOT_AVAILABLE) and policy.authentication (ON_INSTALL, ON_FIRST_USE).

MCP servers execute in project root (at least with project scope). No ${PLUGIN_ROOT} equivalent observed — paths in .mcp.json are relative to project root, not plugin root.

Shared

• .mcp.json — same format, used by both
• skills/ and mcps/ — same files, both platforms read them
• Plugin: test-plugin — one MCP server, one skill
• MCP Server: test-mcp — single-file FastMCP/Python server, run with uv
• Skill: test-skill — calls get_server_info
• Tool: get_server_info — dumps all env vars and CWD

Claude Code behavior

From CLI, not sure if this applies/is shared with claude desktop.

Claude plugin MCP code seems to execute relative to plugin root.

userConfig variables get a new install menu option in claude code, but don't prompt during installation.

Intallation and caching paths:

~/.claude/plugins/marketplaces

• ~/.claude/plugins/installed_plugins.json - contains plugins/scopes/version info
• ~/.claude/plugins/cache/

Logging: ~/Library/Caches/claude-cli-nodejs/-Users-seanlynch-empty/mcp-logs-plugin-test-plugin-test-mcp

Claude Code Dekstop

Claude Desktop seemed to accept the plugins but wouldn't install the MCP server as defined. Not sure if it was the local MCP server or the userconfig.

Claude.ai

• Desktop app, web doesn't support plugins yet
• Despite that, seems to cache these remotely automatically
  1. Plugin lookup by name: https://claude.ai/api/organizations/[organizationUuid]/plugins/by-name/test-plugin?marketplace_name=test-plugin&partition_by =account
  2. Plugin download (ZIP): https://claude.ai/api/organizations/[organizationUuid]/plugins/plugin_[guid]/download

organizationUuid appeared on my personal account despite note being tied to an organization in a ~/Library/Application Support/Claude/local-agent-mode-sessions/[guid]/local_[guid]/.claude/.claude.json

Codex

• project-scoped plugins work in with the CLI, but not with the desktop app
• Desktop app does seem to support user-scoped plugins, though I couldn't get the mcp server to execute propertly
• mcp servers seem to execute in project root (at least with project scope), not plugin root like claude

Logs for CLI stored in

• ~/.codex/log/codex-tui.log

Hack to print pwd

{ "mcpServers": { "pwd-mcp": { "command": "python3", "args": ["-c", "import os; import sys; sys.stderr.write(os.getcwd())"] } } }