# What is a code interpreter?

A code interpreter lets an AI model run code in a live session that keeps variables between runs and returns charts and tables.

**On Runtime every sandbox has one, in seven languages, inside its own
Firecracker microVM.** Python, JavaScript, TypeScript, R, Java, Bash and Go run
as notebook-style sessions, and a new sandbox ran its first Python command
351 ms after the request at the median, measured on 24 September 2026
([speed](/docs/speed)).

## Why AI agents use one

A model is poor at arithmetic and data work in its head, and good at writing
code that does it. A code interpreter closes the loop: the model writes a cell,
the interpreter runs it, and the model reads the output and writes the next
cell. Because state persists, the model can load a file once and then ask ten
questions of it, the way a person works in a notebook.

Running that code needs isolation. The model may have been given a hostile
file, or a prompt injection may tell it to read your secrets. An interpreter
inside a sandbox keeps the damage to a throwaway machine.

## Runtime's code interpreter

| Fact              | Value                                                                           |
| ----------------- | ------------------------------------------------------------------------------- |
| Languages         | Python, JavaScript, TypeScript, R, Java, Bash, Go                               |
| In the image      | Python, JavaScript, TypeScript and Bash; R, Java and Go install on first use    |
| State             | Variables persist between runs; Go keeps functions, types and imports           |
| Rich results      | matplotlib charts and R plots as PNG; pandas and R data frames as tables        |
| Files             | `display` returns a .png, .svg, .html or .csv file as a result, in any language |
| Python data tools | NumPy, pandas and matplotlib in the default image                               |
| Isolation         | A Firecracker microVM with its own kernel; network rules enforced on the host   |

On 23 September 2026 the first use of Java or Go took about 35 seconds and R
about 90, once per sandbox. Bake them into a [custom image](/docs/images) with
`apt` to skip it ([code interpreter](/docs/javascript#code-interpreter)).

## Run a cell

```ts check
import { Sandbox } from "withruntime";

await using sbx = await Sandbox.create({ network: { internet: false } });
await sbx.interpreter.run("import math\nx = math.pi");
const cell = await sbx.interpreter.run("round(x * 2, 3)");
console.log(cell.results[0]?.data["text/plain"]); // 6.283
```

```python check
from withruntime import Runtime

runtime = Runtime()
with runtime.sandboxes.create() as sbx:
    sbx.interpreter.run("import math\nx = math.pi")
    cell = sbx.interpreter.run("round(x * 2, 3)")
    print(cell["results"][0]["data"]["text/plain"])
```

The second cell reads `x` from the first. Pass `{ language: "typescript" }`
(or `language="r"` in Python) to run another language. An agent connected
through MCP gets the same sessions as the `runtime_sandbox_interpreter_run`
tool ([MCP](/docs/mcp#tools)).

## What it costs

The interpreter costs nothing beyond its sandbox. Runtime charges $0.025 per
vCPU-hour of measured CPU and $0.0075 per GiB-hour of memory, so a 2 vCPU,
4 GiB sandbox costs $0.03125 an hour while the model thinks and $0.08 an hour
with both CPUs busy ([pricing](/docs/pricing)). New accounts get 50 free
sandbox hours, no card.

## Related

- [A code interpreter for chatbots](/use-cases/code-interpreter-for-chatbots)
- [A data analysis agent](/use-cases/data-analysis-agent)
- [How to run untrusted code from an LLM safely](/use-cases/run-untrusted-llm-code)
- [What is an agent sandbox?](/glossary/agent-sandbox)

Facts on this page were checked on 25 September 2026.