How do I install the Extend Harness skill?

Run npx skillmds@latest add redpanda-data/extend-harness in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Extend Harness safe to use?

This skill has not completed SkillMD's automated safety review yet. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with Extend Harness?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Extend Harness free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published Extend Harness?

redpanda-data (@redpanda-data) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Extend Harness by redpanda-data — Agent Skill

Name: Extend Harness
Author: redpanda-data

Extend Harness

Extend frontend-skills hook harness. Add new rules via skill-manifest.json, pick severity tier (block/warn/nudge/info/block-strict/diagnostic), view analytics via /frontend-skills-stats. Use when adding enforcement, tuning rule severity, or debugging hook that isn't firing.

redpanda-data d711289 2.9 KB Updated Sep 17, 2026 6 repo stars

File contents

Extend the Harness

1. Never hand-edit generated configs

.claude/settings.json and hooks/hooks.json generated. Edit skill-manifest.json, regenerate:

bash scripts/generate-hook-configs.sh --apply
bash scripts/generate-hook-configs.sh --check   # drift check (lefthook runs this pre-push)

2. Add a new rule (grep-expressible)

Write my-check.sh in .claude/hooks/ -- start from any existing *-check.sh as template.
Add filename to matcher block in skill-manifest.json (usually PostToolUse.Edit|Write).
Regenerate: bash scripts/generate-hook-configs.sh --apply.
Test: feed synthetic edit event on stdin:

echo '{"hook_event_name":"PostToolUse","tool_name":"Edit","tool_input":{"file_path":"/tmp/x.ts"}}' | bash .claude/hooks/my-check.sh

3. Pick the right severity tier

Function	Exit	Claude sees	Logged	Use when
`hook_block`	2	systemMessage	JSONL	Must fix before continuing
`hook_block_strict`	2	`[STRICT]` prefix	JSONL	Security-critical, no escape hatch
`hook_warn`	0	systemMessage	JSONL	Should fix, but proceed
`hook_nudge`	0	`[nudge]` prefix	JSONL	Pattern suboptimal most cases
`hook_info`	0	--	JSONL	Telemetry only, no UI
`hook_emit_diagnostic`	0 or 2	LSP JSON with `range` + `fix`	JSONL	Machine-parseable with auto-fix

Default hook_warn for style, hook_block for correctness, hook_info for observation.

4. When grep isn't enough

Grep can't express nested interactives, exhaustive switches, or useState-object-ref leaks reliably. AST-level patterns: handle in code review for now, or file issue for future Biome custom-rule integration. Don't fake with fragile multi-line regex -- too many false positives.

5. View analytics

/frontend-skills-stats

Reports per-hook P50/P95 latency, blocks/warns/nudges/infos per rule, zero-fire candidates (prune), over-aggressive hooks (soften). Needs >=5 session summaries in ~/.claude/hook-metrics/.

6. Debug a hook that isn't firing

HOOK_DEBUG=1 HOOKS_FAIL_CLOSED=1 claude

Then: tail -f /tmp/hook-session-*/debug.log. Fail-closed turns crash-into-silent-exit into crash-into-visible-block.

7. Verification checklist

skill-manifest.json lists script under correct event+matcher
bash scripts/generate-hook-configs.sh --check exits 0
Script executable (chmod +x)
Sources _hook-lib.sh, parses input, filters extension, handles escape hatch
Test fixture added to evals/ if non-trivial
bash evals/run.sh passes

---name: extend-harnessdescription: Extend frontend-skills hook harness. Add new rules via skill-manifest.json, pick severity tier (block/warn/nudge/info/block-strict/diagnostic), view analytics via /frontend-skills-stats. Use when adding enforcement, tuning rule severity, or debugging hook that isn't firing.---# Extend the Harness## 1. Never hand-edit generated configs`.claude/settings.json` and `hooks/hooks.json` generated. Edit `skill-manifest.json`, regenerate:```bashbash scripts/generate-hook-configs.sh --applybash scripts/generate-hook-configs.sh --check # drift check (lefthook runs this pre-push)```## 2. Add a new rule (grep-expressible)1. Write `my-check.sh` in `.claude/hooks/` -- start from any existing `*-check.sh` as template.2. Add filename to matcher block in `skill-manifest.json` (usually `PostToolUse.Edit|Write`).3. Regenerate: `bash scripts/generate-hook-configs.sh --apply`.4. Test: feed synthetic edit event on stdin:```bashecho '{"hook_event_name":"PostToolUse","tool_name":"Edit","tool_input":{"file_path":"/tmp/x.ts"}}' | bash .claude/hooks/my-check.sh```## 3. Pick the right severity tier| Function | Exit | Claude sees | Logged | Use when ||---|---|---|---|---|| `hook_block` | 2 | systemMessage | JSONL | Must fix before continuing || `hook_block_strict` | 2 | `[STRICT]` prefix | JSONL | Security-critical, no escape hatch || `hook_warn` | 0 | systemMessage | JSONL | Should fix, but proceed || `hook_nudge` | 0 | `[nudge]` prefix | JSONL | Pattern suboptimal most cases || `hook_info` | 0 | -- | JSONL | Telemetry only, no UI || `hook_emit_diagnostic` | 0 or 2 | LSP JSON with `range` + `fix` | JSONL | Machine-parseable with auto-fix |Default `hook_warn` for style, `hook_block` for correctness, `hook_info` for observation.## 4. When grep isn't enoughGrep can't express nested interactives, exhaustive switches, or useState-object-ref leaks reliably. AST-level patterns: handle in code review for now, or file issue for future Biome custom-rule integration. Don't fake with fragile multi-line regex -- too many false positives.## 5. View analytics```/frontend-skills-stats```Reports per-hook P50/P95 latency, blocks/warns/nudges/infos per rule, zero-fire candidates (prune), over-aggressive hooks (soften). Needs >=5 session summaries in `~/.claude/hook-metrics/`.## 6. Debug a hook that isn't firing```bashHOOK_DEBUG=1 HOOKS_FAIL_CLOSED=1 claude```Then: `tail -f /tmp/hook-session-*/debug.log`. Fail-closed turns crash-into-silent-exit into crash-into-visible-block.## 7. Verification checklist- [ ] `skill-manifest.json` lists script under correct event+matcher- [ ] `bash scripts/generate-hook-configs.sh --check` exits 0- [ ] Script executable (`chmod +x`)- [ ] Sources `_hook-lib.sh`, parses input, filters extension, handles escape hatch- [ ] Test fixture added to `evals/` if non-trivial- [ ] `bash evals/run.sh` passes

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