Code Mode: flat token cost for big MCP catalogs

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
discover_tools	Finds the tools that fit the task and returns their TypeScript signatures
execute_code	Executes JavaScript code containing toolmesh.* function calls

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

Discovery scales with the catalog. discover_tools narrows by regex pattern or BM25-ranked free-text query, and its detail level follows the number of matches on its own: up to 25 matches it returns full TypeScript signatures, up to 250 one-line summaries, and beyond that names only or a per-backend overview. Every response closes with a matched/shown count and a hint for refining; detail and limit override the automatic choice. Inside execute_code the same index is reachable as toolmesh.discover("<free text>") and toolmesh.describe("<tool_name>"), so a script can look up a signature mid-run without spending a round-trip.

Note

This tool was called list_tools before ToolMesh v0.4.0. The rename has no backwards-compatible alias — a client that hard-codes the old name gets a tool-not-found error.

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

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

Example

// LLM generates this after calling discover_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.