---
description: "Package map for the code-execution capability family: what program execution does for you, and which package owns each part."
kind: "package-group"
---

# code-runtime/ — code-execution capability family

English | [中文](README.zh.md)

## Summary

The `code-runtime/` group lets a model write one program that calls host-provided functions as ordinary async calls, then returns only the program's printed output and return value. Choose the TypeScript backend for execution in an isolated Node worker, or the experimental Python backend when a CPython process is required. Each run starts without state from earlier programs. Failures are returned as results so callers can diagnose them or provide them to the model.

## Table of Contents

- [Packages](#packages)
- [Related documentation](#related-documentation)
- [Dev Note](#dev-note)

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<a id="packages"></a>
## Packages

These three packages together provide program execution; each README describes what its part does.

| Package | Role | ctx key |
|---|---|---|
| [`code-runtime/`](code-runtime/README.md) | Defines what a code runtime does: run one program against host-provided bindings and report what it printed and returned | `ctx.codeRuntime` |
| [`code-runtime-worker-thread/`](code-runtime-worker-thread/README.md) | Executes TypeScript programs, each in a fresh Node worker thread | registers `ctx.codeRuntime` |
| [`experimental/code-runtime-python/`](../experimental/code-runtime-python/README.md) | The experimental Python backend: owns the fd-3 wire protocol between a Node host and a CPython subprocess and the CPython runtime implementation | — |

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<a id="related-documentation"></a>
## Related documentation

Start with the subsystem reference for the service contract, then the PTC mode design that consumes this capability and the capability-seam model it follows.

- [Code runtime subsystem reference](../../docs/subsystems/code-runtime.md) — request/result vocabulary, bindings, and the `ctx.codeRuntime` cordis surface.
- [PTC mode Agent Note](../../.agents/notes/implemented/feature/2026-06-15-ptc.md) — how the tool registry presents `run_code` to the model.
- [Capability seams](../../docs/capability-seams.md) — the Service Definition / Service Provider / Consumer split this family follows.

<a id="dev-note"></a>
## Dev Note

<details>
<summary>Working context for maintainers — click to expand</summary>

None.

</details>