# Code Mode: flat token cost for big MCP catalogs

> Code Mode replaces a 50,000-token MCP tool list with two meta-tools (list_tools + execute_code) and a TS interface. ~1,000 tokens cover any catalog size.

Canonical: https://www.toolmesh.io/en/code-mode/

Connect 15 MCP servers to a single AI agent? Without ToolMesh, that simply does not work — the context window fills up, the client chokes. Code Mode makes it possible by replacing hundreds of tool definitions with two meta-tools and a compact TypeScript interface.

## How It Works

ToolMesh exposes two meta-tools:

| Tool | Purpose |
|------|---------|
| `list_tools` | Returns all available tools with TypeScript interface definitions |
| `execute_code` | Executes JavaScript code containing `toolmesh.*` function calls |

The LLM calls `list_tools` once, sees the available functions with their type signatures, then writes JavaScript that chains multiple calls together.

## Why Code Mode?

### Scaling That Otherwise Doesn't Work

Every tool in the MCP tool list costs context window budget. With 50+ tools from multiple backends, the context window fills up and the client becomes unusable. Code Mode reduces 50,000+ tokens to ~1,000 — the difference between "doesn't work" and "just runs."

### Fewer Round-Trips

Instead of:

```
LLM → tool_a → result → LLM → tool_b(result) → result → LLM → tool_c(result)
```

Code Mode enables:

```
LLM → execute_code("let a = await tool_a(); let b = await tool_b(a); return tool_c(b);")
```

One round-trip instead of three.

### Type Safety

`list_tools` returns TypeScript interfaces, so the LLM generates well-typed code that the AST parser can validate before execution.

## Example

```javascript
// LLM generates this after calling list_tools
const repos = await toolmesh.github_list_repos({ sort: "updated" });
const issues = [];
for (const repo of repos.slice(0, 3)) {
  const repoIssues = await toolmesh.github_list_issues({
    owner: repo.owner.login,
    repo: repo.name,
    state: "open"
  });
  issues.push(...repoIssues);
}
issues
```

## Security

Code Mode uses AST parsing to ensure only `toolmesh.*` function calls are executed. The JavaScript runs in a sandboxed environment with no access to `fetch()`, `require()`, the filesystem, or any globals beyond the `toolmesh` namespace.

## Origin

Code Mode was pioneered by Cloudflare for their own API. ToolMesh brings it to any backend — MCP servers and DADL-described REST APIs alike.