Efficiently connect agents and APIs with “code mode” on Blaxel

Token efficiency is an important topic for AI developers these days.

The more tools you give an AI agent, the more information it has to deal with, and the higher the token count. This is both inefficient and expensive.

“Code mode”, first proposed in a Cloudflare blog post, is an innovative answer to this problem. A subsequent Anthropic blog post about a similar idea, "code execution over MCP", explains why this approach offers significant token savings over traditional MCP tool calling methods.

"Code mode" is now natively supported on Blaxel for OpenAPI-compatible APIs. With this, you can expose any OpenAPI specification to your agents as an MCP server hosted on Blaxel.

How it works

1. Use the Blaxel CLI to deploy an MCP server in code mode. Replace the OPENAPI_REFERENCE variable with your OpenAPI specification URL.

   bl apply -f - <<EOF
   apiVersion: blaxel.ai/v1alpha1
   kind: Function
   metadata:
     displayName: Petstore API Code Mode
     name: petstore-code-mode
   spec:
     runtime:
       type: mcp
       image: blaxel/code-mode:latest
       memory: 2048
       envs:
         - name: OPENAPI_REFERENCE
           value: https://petstore3.swagger.io/api/v3/openapi.json
   EOF
   

2. Retrieve the MCP server's endpoint url:

   bl get mcp my-api-code-mode -o json | jq -r '.[] | .metadata.url'
   

3. Feed this URL to your agent to have it connect to the MCP server as usual and start using the API.

The two tools available are search, which enables an AI agent to evaluate the OpenAPI specification, and execute, which enables the agent to run JavaScript code that calls the actual API endpoints needed for the requested task. All the agent-generated code runs inside an auto-scaling sandbox with a 10-minute idle TTL, ensuring complete isolation and security.

API authentication

API authentication is fully supported. For example, if the target OpenAPI specification defines an authentication scheme called ApiKeyAuth, authenticate against the API by defining an environment variable in your MCP deployment schema called AUTH_APIKEYAUTH with the corresponding secret:

    envs:
      - name: OPENAPI_REFERENCE
        value: https://api.example.com/openapi.json
      - name: AUTH_APIKEYAUTH
        value: ${secrets.AUTH_APIKEYAUTH}

Read more about our implementation of code mode and then try it out for yourself: we've put together a tutorial about using a Claude SDK agent in code mode with Blaxel. All you need is your Anthropic API key, a Blaxel account, and the Blaxel CLI.

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