Agent Harness SDK

Agent Harness SDK wraps Claude Code in a deterministic shell — three TypeScript primitives, enforced by Claude Code's hooks:

• Guards — pre-action policies. Block bad calls before they run.
• Checks — post-action validators. Catch problems and feed them back.
• Tools — deterministic MCP operations. Replace error-prone prose steps.

See How it works for the agentic-loop walkthrough.

Getting Started

Install

npm install -D agent-harness-sdk
npx harness init

Restart Claude Code. You will now have a harness/ directory, hooks registered under .claude/, and the harness server merged into .mcp.json.

Scaffold a primitive

From inside Claude Code:

/harness add guard block-pushes
/harness add check validate-routes
/harness add tool fetch-weather

Each command writes a typed stub into the right directory and registers it in harness/harness.config.ts. Fill in the run/handler body and you're done.