mcp-slim-guard — Claude Code MCP server: what it does, how to install
mcp-slim-guard narrows access to approved MCP tools, checks calls before dispatch, and restores large results without invoking the upstream tool again.
claude mcp add mcp-slim-guard -- npx -y mcp-slim-guardWhat mcp-slim-guard does
mcp-slim-guard gives an MCP host a controlled route to approved upstream tools. It retains their original argument schemas, applies allow and deny rules, and validates each call before the upstream server is contacted. In Compact and Extreme, discovery returns up to three authorized matches with their required fields, enums, and nested schema.
Compact exposes find_tool, call_tool, and read_result, and is the default for Claude Code. Native keeps the regular authorized catalog, while Extreme shortens the first delivery only when the response is large enough for that boundary. A captured result can be read through bounded fragments or an exact snapshot, with no second upstream call.
A reviewed checkout needs npm ci, npm run build, and npm link; initialization then creates mcp-slim-guard.yml with version 2. Version 1 configuration is rejected. The project is alpha, so authorization rules and upstream settings need review before privileged tools are connected.
What it helps with
- restrict MCP tools with allow and deny rules
- validate arguments before an upstream call
- reduce the first delivery of a large result
- recover an exact snapshot without rerunning the tool
- search only the authorized tool catalog
Example prompts for the agent
- Use
find_toolto locate an approved task-management tool and inspect its schema. - Call the selected upstream tool through
call_tool, using arguments that match its original schema. - Use
read_resultwith the returnedresult_refandnext_cursorto recover a large response.
How to install mcp-slim-guard
Platform CLI
claude mcp add mcp-slim-guard -- npx -y mcp-slim-guardPlatform CLI
codex mcp add mcp-slim-guard -- npx -y mcp-slim-guardConfig file
{
"mcpServers": {
"mcp-slim-guard": {
"command": "npx",
"args": [
"-y",
"mcp-slim-guard"
]
}
}
}Config file
{
"servers": {
"mcp-slim-guard": {
"type": "stdio",
"command": "npx",
"args": [
"-y",
"mcp-slim-guard"
]
}
}
}Platform CLI
gemini mcp add mcp-slim-guard npx -y mcp-slim-guardStep by step, with commands for each platform: How to add an MCP server to Claude Code, Codex, Cursor, VS Code, Gemini CLI and more
Questions about mcp-slim-guard
How do I install mcp-slim-guard in Claude Code?
Run claude mcp add mcp-slim-guard -- npx -y mcp-slim-guard. When running from a checkout, first use npm ci, npm run build, and npm link.
What does mcp-slim-guard do?
It limits the MCP catalog to authorized tools, validates arguments against each original schema before dispatch, and can recover a large result without calling the upstream tool again.
Which modes does mcp-slim-guard support in Claude Code?
Claude Code supports Compact and Extreme installation plans. Native is not supported there, and Compact is the default mode.
