add-harness-package

Adding a New Harness Package

This guide covers creating a new @ai-sdk/harness-<name> package for an agent harness.

A harness can be host-driven, where the runtime runs in the host process and uses the sandbox remotely, or bridge-backed, where a small bridge runs inside the sandbox because the runtime needs local access to the sandbox filesystem or process environment. Prefer host-driven when the runtime supports it.

First-Party vs Third-Party Harnesses

• Third-party packages: Any runtime can publish an external harness package.
• First-party @ai-sdk/harness-<name> packages: Create an issue first to discuss whether the runtime belongs in this repo.

Reference Example

See https://github.com/vercel/ai/pull/16255/changes for a complete example of adding a new harness.

Harness Architecture

The AI SDK uses a layered harness architecture following the adapter pattern: