Claude Code skill: add code mode to any MCP server for 65-99% context reduction
Overview
An agent skill that helps you add to any MCP server — so LLMs can write small processing scripts that run against large API responses in a sandboxed runtime, and only the script's compact output enters the context window. Works with any AI agent that supports agent skills. When an MCP tool returns a large API response (e.g. listing 500 Kubernetes pods, 200 SCIM users, or thousands of GitHub issues), that entire payload enters the LLM's context window — consuming tokens and degrading performance. Code mode flips the approach: instead of dumping raw data into context, the LLM writes a small processing script. The MCP server runs the script in a against the raw data, and only the script's stdout enters context. This works especially well with well-known APIs (SCIM, Kubernetes, GitHub, Stripe, Slack, AWS, etc.) because LLMs already know the response schemas from training data. Inspired by Cloudflare Code Mode and claude-context-mode. This is an .
README
Code Mode Skill
An agent skill that helps you add code mode to any MCP server — so LLMs can write small processing scripts that run against large API responses in a sandboxed runtime, and only the script’s compact output enters the context window. Works with any AI agent that supports agent skills.
Typical result: 65–99% context reduction.
What is Code Mode?
When an MCP tool returns a large API response (e.g. listing 500 Kubernetes pods, 200 SCIM users, or thousands of GitHub issues), that entire payload enters the LLM’s context window — consuming tokens and degrading performance.
Code mode flips the approach: instead of dumping raw data into context, the LLM writes a small processing script. The MCP server runs the script in a sandboxed runtime against the raw data, and only the script’s stdout enters context.
This works especially well with well-known APIs (SCIM, Kubernetes, GitHub, Stripe, Slack, AWS, etc.) because LLMs already know the response schemas from training data.
Inspired by Cloudflare Code Mode and claude-context-mode.
What This Skill Does
This is an interactive planning skill. It works with you step-by-step to:
- Understand your MCP server (language, framework, which tools return large data)
- Select a sandbox that fits your server language and security requirements
- Plan the implementation together
- Implement the code mode tool, sandbox executor, and wiring
- Benchmark before/after context sizes to verify the reduction
Supported Server Languages
| Server Language | Sandbox Options |
|---|---|
| TypeScript/JavaScript | quickjs-emscripten (WASM), pyodide (WASM), isolated-vm (V8) |
| Python | RestrictedPython, pyodide (WASM), quickjs bindings |
| Go | goja, Wazero (WASM), starlark-go |
| Rust | boa_engine, wasmtime/wasmer (WASM), deno_core |
All sandbox options are isolated from the host filesystem and network by default.
Install
npx skills add chenhunghan/code-mode-skill
Or manually copy the SKILL.md and references/ directory into your agent’s skills directory.
Usage
Just ask your agent to add code mode to your MCP server:
- “I want to add code mode to my MCP server to reduce token usage”
- “Add a sandboxed code execution tool to my TypeScript MCP server”
- “My get-users tool returns 50KB+ responses, help me reduce context size”
The skill will guide you through the process interactively.
License
MIT
Recommended Tools
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Install
npx skillfish add chenhunghan/code-mode-skill