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Claude Code plugin named /harness is built for Fable 5 and runs your agent…

2026-06-10 · 18:24 UTC ·@hyperbrowser ·0 min read

Brief

The /harness plugin for Fable 5 (by @hyperbrowser) executes your agent against your codebase, monitors build/runtime failures, and auto-generates a CLAUDE.md from the observed errors. It specifically detects wrong paths, missing scripts, and faulty assumptions so agents can learn from concrete failures and avoid repeating identical mistakes; a video demo accompanies the announcement.

Why it matters

Claude Code plugin named /harness is built for Fable 5 and runs your agent against your actual project to observe runtime failures.

Key details

  • /harness records real failure evidence into a CLAUDE.md file (from wrong paths, missing scripts, and bad assumptions) so the agent avoids repeating the same errors.
  • Author @hyperbrowser demonstrated the tool with a short video showing it watches the project break and generates actionable failure docs.
Source evidence

/harness

A Claude Code plugin built for Fable 5. It runs your agent against your project, watches it break, and writes a CLAUDE. md from the actual failures.

It catches wrong paths, missing scripts, and bad assumptions so your agent never hits the same wall twice ↓

Video