How Code Executors Work

Understanding API interception and URL transformation

Overview

Code executors wrap your agent’s code and intercept API calls. They allow your AI agent to write normal code targeting production APIs (like https://slack.com/api/*) while actually hitting isolated test environments.

Flow

1. Agent Writes Code

   requests.post('https://slack.com/api/chat.postMessage', json={...})
   
2. Code executor Proxy

   1. Wraps code with interception logic
   2. Detects API URL patterns
   3. Rewrites URLs to route into the isolated environment

   https://slack.com/api/* 
       → http://localhost:8000/api/env/{env_id}/services/slack/*
   
3. Environment

   Real API responses from your sandboxed environment

URL Transformation Rules

The executor transforms URLs based on these patterns:

Original URL	Transformed URL
https://slack.com/api/*	http://localhost:8000/api/env/{id}/services/slack/*
https://api.slack.com/api/*	http://localhost:8000/api/env/{id}/services/slack/*
https://api.linear.app/*	http://localhost:8000/api/env/{id}/services/linear/*

Available Executors

Python

Intercepts requests and urllib

TypeScript

Intercepts fetch API

Bash

Intercepts curl commands

How Interception Works

Python Executor

The Python executor wraps code with a custom URL opener:

# What gets prepended to your code:
import urllib.request
import urllib.parse
from urllib.request import Request, urlopen

_original_urlopen = urllib.request.urlopen

def _intercepting_urlopen(url, *args, **kwargs):
    if isinstance(url, str):
        url = _transform_url(url)
    elif hasattr(url, 'full_url'):
        url.full_url = _transform_url(url.full_url)
    return _original_urlopen(url, *args, **kwargs)

urllib.request.urlopen = _intercepting_urlopen

# Also patches requests library
import requests
_original_request = requests.Session.request

def _intercepting_request(self, method, url, *args, **kwargs):
    return _original_request(self, method, _transform_url(url), *args, **kwargs)

requests.Session.request = _intercepting_request

TypeScript Executor

The TypeScript executor overrides global fetch:

// What gets prepended to your code:
const originalFetch = globalThis.fetch;

globalThis.fetch = async (url: string | URL, init?: RequestInit) => {
  const transformedUrl = transformUrl(url.toString());
  return originalFetch(transformedUrl, init);
};

Bash Executor

The Bash executor uses sed to transform curl URLs:

# Original curl command:
curl https://slack.com/api/chat.postMessage -d '{"text":"hello"}'

# Transformed:
curl http://localhost:8000/api/env/{id}/services/slack/chat.postMessage -d '{"text":"hello"}'

Security Considerations

Code executors run arbitrary code. In production, consider:

• Running executors in sandboxed containers
• Implementing timeouts
• Restricting network access
• Validating code before execution

Next Steps

Python Executor

Detailed Python executor guide

TypeScript Executor

Detailed TypeScript executor guide