Agent skill · software engineering · vercel
add-harness-package
Guide for adding new AI SDK harness packages. Use when creating a new @ai-sdk/harness-<name> package that adapts a coding-agent runtime to HarnessV1.
Why this skill is useful
Provides specific package structure and configuration details for creating new AI SDK harness packages that the AI wouldn't reliably generate on its own.
What it needs
Requires pnpm installed locally. About 7k tokens when loaded. Last updated 2026-08-07. 26,057 stars on the source repository.
What this skill does
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: 1. Harness specification (@ai-sdk/harness): Defines interfaces like HarnessV1 and HarnessV1Session 2. Utilities (@ai-sdk/harness/utils): Shared code for implementing harnesses 3. Harness implementations (@ai-sdk/harness-<name>): Concrete adapters for harnesses 4. Harness agent (@ai-sdk/harness/agent): The high-level user-facing HarnessAgent API Step-by-Step Guide 1. Create Package Structure Create packages/harness-<name> with this baseline structure: If the runtime must execute inside the sandbox, add bridge files as well: Add a CHANGELOG.md containing just the package heading (# @ai-sdk/harness-<name>). Every package is required to have one. 2. Configure package.json Use existing harness packages as the source of truth for scripts, exports, repository metadata, and publish settings. …
How to use it
Reference it in AdaL, Claude Code, Cursor or any coding agent — nothing to install:
@skills vercel/add-harness-package