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Agent Skill

Add Harness Package skill

add-harness-packagevercel/aiskills/add-harness-package/SKILL.md

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.

27k

always on

41 tokname + description

once used

2,881 tokSKILL.md body

bundled files

14 KB

repo stars

27kGitHub

Install the Add Harness Package skill

Skills CLI (Claude Code, Codex, Cursor and others)

npx skills add https://github.com/vercel/ai --skill add-harness-package

Claude Code, by hand (all projects)

git clone --depth 1 https://github.com/vercel/ai.git /tmp/ai
mkdir -p ~/.claude/skills
cp -R /tmp/ai/skills/add-harness-package ~/.claude/skills/add-harness-package

For one project only, copy the folder into .claude/skills/ in that project instead. The agent picks it up when a task matches its description.

What it costs your context

Agent Skills load in three steps. Tokens counted with the o200k tokenizer; your model's count will differ a little.

WhenWhat loadsCost
Every sessionName and description41 tok
When the agent uses itThe SKILL.md instructions2,881 tok
Only if opened1 bundled files (4 KB)varies

Until it is used, add-harness-package costs about 33× less than the median MCP server we measured (1,362 tokens on every turn). Installing all 14 skills from vercel/ai would load 683 tokens of descriptions. Skills vs MCP study

Checks

Our checks found nothing to flag: it follows the Agent Skills specification's naming and size guidelines and doesn't pipe downloads into a shell.

Checked 2026-10-22 · method

What's inside

The headings of its SKILL.md. Read the full file on GitHub.

  • Adding a New Harness Package
  • First-Party vs Third-Party Harnesses
  • Reference Example
  • Harness Architecture
  • Step-by-Step Guide
  • 1. Create Package Structure
  • 2. Configure package.json
  • 3. Create TypeScript, Build, and Test Configs
  • 4. Implement the Harness Adapter
  • 5. Implement Runtime-Specific Concerns
  • 6. Write Tests
  • 7. Add README
  • 8. Add Examples
  • 9. Add Documentation
  • 10. Update References and Validate
  • Checklist
  • Related Documentation

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