techlist.io
KREN
cloudflare

Code Mode: give agents an entire API in 1,000 tokens (opens in new tab)

ai-agentmodel-context-protocoljavascriptcloudflare-workersopenapicode-executioncontext-window-optimization

Code Mode addresses a central MCP problem: giving agents broad tool access without overwhelming their context windows. Instead of exposing thousands of individually described tools, it provides a typed SDK and lets agents write sandboxed JavaScript to search specifications and execute API calls. Cloudflare’s new MCP server applies this approach to its entire API using only search() and execute(), reducing context usage by 99.9% to roughly 1,000 tokens.

The Context-Window Problem

  • MCP makes external tools available to AI agents, but each tool’s description consumes model context.
  • Large APIs can require enormous token budgets merely to describe their endpoints.
  • A conventional MCP server for the Cloudflare API would consume approximately 1.17 million tokens.
  • This can exceed the context window of even advanced foundation models.

Code Mode as a Compact API Interface

  • Agents write code against a typed SDK rather than selecting from thousands of separate tools.
  • Generated code serves as a compact, composable plan.
  • Agents can:
    • Explore available operations.
    • Chain multiple API calls.
    • Handle pagination and errors.
    • Return only the data needed for the task.
  • The tool footprint remains fixed as the underlying API grows.

Cloudflare’s Two-Tool MCP Server

  • The server exposes only:
    • search() — searches the Cloudflare OpenAPI specification.
    • execute() — runs JavaScript against the Cloudflare API.
  • The full OpenAPI specification stays outside the model context.
  • $refs are pre-resolved, allowing agents to inspect endpoint metadata directly through code.
  • Agents can filter endpoints by product, path, tags, or other metadata.

Sandboxed Execution

  • Both tools execute code inside a Dynamic Worker isolate based on lightweight V8 sandboxes.
  • The environment has:
    • No filesystem access.
    • No environment variables exposed to generated code.
    • External fetches disabled by default.
  • Outbound requests can be explicitly enabled through controlled fetch handlers.

Example: Finding DDoS Protection Endpoints

  • For a request to protect an origin from DDoS attacks, an agent can first consult documentation or skills.
  • It then uses search() to inspect the OpenAPI specification.
  • A JavaScript query can locate zone endpoints related to WAF and rulesets.
  • The search narrows more than 2,500 Cloudflare endpoints to relevant operations such as:
    • Listing and updating WAF packages and rules.
    • Listing and creating zone rulesets.
    • Reading and updating entry-point rulesets.
    • Creating and updating rules within a ruleset.
  • Once the relevant endpoints are identified, execute() can perform coordinated API requests in one sandboxed run.

SDK Availability

  • Cloudflare is open-sourcing a Code Mode SDK as part of the Cloudflare Agents SDK.
  • The same pattern can be used to build more context-efficient MCP servers and AI agents.

Code Mode is most useful for large, evolving APIs: expose a small, stable tool surface, let agents discover capabilities programmatically, and execute only the focused operations required for each task.