← AI Agents & MCP theorytheory 0/14 · 0%

level 1

Curious · 0 XP

streak

perfect

badges

100 XP to Apprentice

Tools · medium

10. Sandboxed code execution

The most powerful agent tool, and the most dangerous.

1 min read2 questionsup to 50 XPtopic 10/14

Read in another language

AI translates the explanation and quiz text while preserving code and answer scoring.

Letting an agent write and run code turns vague tasks into solvable ones — data analysis, format conversion, scraping. It also hands untrusted output an execution surface.

Non-negotiable controls:

- Run in an isolated container or microVM, never the app process. - No credentials in the sandbox environment. - Deny egress by default; allow-list specific hosts. - Wall-clock, memory, and disk limits; destroy the sandbox after the run. - Mount inputs read-only and collect outputs from a dedicated directory.

ts
const sandbox = await createSandbox({ image: "python:3.12-slim", timeoutMs: 30_000, network: "none" });
try {
  const { stdout, stderr, exitCode } = await sandbox.run("python", ["-c", code]);
  return { stdout: stdout.slice(0, 8_000), stderr: stderr.slice(0, 2_000), exitCode };
} finally {
  await sandbox.destroy();
}

Feed `stderr` back to the model: a self-correcting write-run-fix loop with two retries fixes most first-attempt errors, and truncating output protects the context window.

Exercise: give the agent a messy CSV and ask for the median of a column. Verify from logs that it executed code rather than estimating the answer.

How to study this topic

1. Read the explanation once end to end, skipping the code.
2. Re-read the code snippets and say out loud what each line does.
3. Answer the quiz without scrolling back — that is the real check.
4. Read every explanation, even for the answers you got right.

Scoring

· Up to 30 XP from quiz accuracy.
· +15 XP for a perfect first attempt.
· +5 XP while a 3-day streak is running.
· 75% or higher marks the topic complete.

Check your understanding

1. Where should agent-written code run?
In an isolated sandbox with no credentials and no default egressIn the API server processIn the browserIn the database
2. Why return stderr to the model?
It enables a self-correcting fix-and-retry loopIt reduces costIt is required by the sandboxIt prevents injection

Badges

First light

Pass your first topic

Sharp shooter

3 perfect first-try quizzes

On a roll

Study 3 days in a row

Week warrior

Study 7 days in a row

Grinder

Earn 500 XP

Deep diver

Earn 1500 XP