Context Engineering & Harness Engineering Toolkit for Claude Code

Structured prompts, agent orchestration, and automated pipelines — debugging, code review, UI design, product specs, and more.

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Install

npx devlyn-cli

That's it. The interactive installer handles everything. Claude Code config is installed by default; optional AI CLI instructions can be selected during install. Choose Codex CLI (OpenAI) to install AGENTS.md AND /devlyn:resolve + /devlyn:ideate + /devlyn:design-ui skills into ~/.codex/skills/ so the same slash commands work inside Codex too. Run it again anytime to update.

How It Works — Two Skills, Full Cycle

devlyn-cli turns Claude Code into a hands-free development pipeline. The pipeline surface is two skills, with /devlyn:design-ui installed as the required creative UI surface:

ideate (optional)  →  resolve  →  ship

Step 1 (optional) — Plan with /devlyn:ideate

Turn a raw idea into a verifiable spec — single-feature, multi-feature, or "normalize this external doc".

/devlyn:ideate "I want to build a habit tracking app with AI nudges"

Default mode produces a docs/specs/<id>-<slug>/spec.md plus spec.expected.json (mechanical verification block) that /devlyn:resolve --spec consumes directly. Modes:

| Mode | When to use | |---|---| | default | One feature, AI drives focused Q&A | | --quick | One-line goal → assume-and-confirm spec, single-turn (autonomous-pipeline-safe) | | --from-spec <path> | You already wrote a spec; ideate normalizes + lints it | | --project | Multi-feature project: emits plan.md index + N child specs |

Skip ideate entirely if you have a spec or just want to describe the work — /devlyn:resolve accepts free-form goals too.

Step 2 — Resolve with /devlyn:resolve

Hands-free pipeline for any coding task — bug fix, feature, refactor, debug, modify, PR review. Pass a spec, a free-form goal, or a diff to verify.

/devlyn:resolve "fix the login bug"                                # free-form
/devlyn:resolve --spec docs/specs/2026-05-04-auth/spec.md          # spec mode
/devlyn:resolve --verify-only <diff-or-PR-ref> --spec <path>       # verify-only

Internal phases run sequentially with file-based handoff via .devlyn/pipeline.state.json:

PLAN  →  IMPLEMENT  →  BUILD_GATE  →  CLEANUP  →  VERIFY (fresh subagent, findings-only)

• PLAN is the heaviest phase by design — formalizes invariants from the spec/goal and the file list to touch.
• BUILD_GATE runs your project's real compilers, typecheckers, linters, and python3 .claude/skills/_shared/spec-verify-check.py (verification commands literal-match). Auto-detects Next.js, Rust, Go, Solidity, Expo, Swift, and Dockerfiles. Browser flows route through Chrome MCP → Playwright → curl tier.
• VERIFY runs in a fresh subagent context with no code-mutation tools — findings only, structurally independent.
• Git checkpoints at every phase for safe rollback. Fix-loop budget shared across BUILD_GATE and VERIFY (--max-rounds N, default 4).

Common flags: --engine claude|codex|auto (default claude), --bypass build-gate,cleanup, --pair-verify (force pair-mode JUDGE in VERIFY), --no-pair (intentional solo VERIFY), --risk-probes / --no-risk-probes, --perf (per-phase timing). --pair-verify and --no-pair are mutually exclusive; using both stops with BLOCKED:invalid-flags.

Free-form goals that ask for benchmark evidence, pair-evidence, risk-probe measurement, solo<pair proof, or solo-headroom work must include an actionable solo-headroom hypothesis naming the visible behavior solo_claude is expected to miss plus a backticked observable command; the backticked line itself must contain miss and be framed as the command/observable that exposes it. Without that, /devlyn:resolve stops with BLOCKED:solo-headroom-hypothesis-required and points you to /devlyn:ideate instead of inventing a weak hypothesis. Free-form goals that add or run a new unmeasured benchmark, shadow fixture, golden fixture, risk-probe, or pair-evidence candidate must also include solo ceiling avoidance, mention solo_claude, and name the concrete difference from rejected or solo-saturated controls such as S2-S6; without that, /devlyn:resolve stops with BLOCKED:solo-ceiling-avoidance-required.

Engine selection — Claude implementation, conditional pair VERIFY

--engine claude (default) is the canonical implementation surface for PLAN, IMPLEMENT, BUILD_GATE, and CLEANUP. VERIFY/JUDGE conditionally runs pair mode for verify-only runs, high-risk specs, risk probes, mechanical warnings, coverage gaps, or explicit --pair-verify.

--engine codex routes IMPLEMENT to Codex; --engine auto opts into the experimental dual-engine routing where applicable. Both are research-only at HEAD: iter-0020 closed Codex BUILD/IMPLEMENT below the quality floor on the 9-fixture suite (L2 vs L1 = −3.6, 3/8 gated fixtures cleared the +5 margin floor — release-readiness FAIL); iter-0033g + iter-0034 closed PLAN-pair as research-only with explicit unblock conditions (container/sandbox infra OR production telemetry capturing positive evidence of subagent introspection). Install the Codex CLI (https://platform.openai.com/docs/codex) and pass the flag explicitly to opt in:

/devlyn:resolve "fix the auth bug" --engine auto   # experimental, research-only

If Codex or Claude is absent when explicitly selected or conditionally required, the harness stops with BLOCKED:codex-unavailable or BLOCKED:claude-unavailable and prints setup guidance. Use --no-pair only when intentionally accepting solo VERIFY; use --no-risk-probes only when intentionally disabling automatic high-risk probes.

Benchmark score runs

Use the benchmark CLI when a change claims solo_claude < pair. The score-focused runners print the run id, startup gate lines, blind-judge score tables, fixture pair margins, average pair margin, wall-time ratio, and failure reasons:

npx devlyn-cli benchmark headroom --min-fixtures 3 F16-cli-quote-tax-rules F23-cli-fulfillment-wave F25-cli-cart-promotion-rules
npx devlyn-cli benchmark recent
npx devlyn-cli benchmark recent --out-md /tmp/devlyn-recent-benchmark.md
npx devlyn-cli benchmark frontier --out-md /tmp/devlyn-pair-frontier.md
npx devlyn-cli benchmark audit --out-dir /tmp/devlyn-benchmark-audit
npx devlyn-cli benchmark audit-headroom --out-json /tmp/devlyn-headroom-audit.json
npx devlyn-cli benchmark pair --min-fixtures 3 --max-pair-solo-wall-ratio 3 F16-cli-quote-tax-rules F23-cli-fulfillment-wave F25-cli-cart-promotion-rules

benchmark recent prints a compact, wrap-safe snapshot of the current local pair evidence: status counts, pair-lift aggregates, and one card per passing pair-evidence fixture. It intentionally avoids wide Markdown tables, so the same output stays readable in narrow terminals, PR comments, and release notes. benchmark frontier also prints a stdout score summary for existing complete pair evidence rows, including pair arm, trigger reasons, average/minimum pair margin, and wall ratio, plus row-level verdicts even when --out-json or --out-md writes an artifact. Markdown frontier artifacts include a Triggers column. Full-pipeline pair gate artifacts record require_hypothesis_trigger in JSON and include a Markdown Hypothesis trigger column, so strict regenerated evidence shows whether each row carried spec.solo_headroom_hypothesis. benchmark audit is the provider-free release/handoff guard: it writes audit.json with the frontier summary, artifact map, and compact trigger-backed verdict-bearing pair_evidence_rows (each row carries pair_trigger_eligible: true, non-empty pair_trigger_reasons, pair_trigger_has_canonical_reason: true, and pair_trigger_has_hypothesis_reason; the audit fails rows missing trigger reasons or missing actionable solo-headroom hypotheses in fixture spec.md whose observable command matches expected.json), runs the frontier with --fail-on-unmeasured, requires at least four fixtures with passing pair evidence, revalidates frontier verdict: PASS, zero unmeasured candidates, and revalidates pair_mode: true, the default 5-point pair margin, and 3x pair/solo wall ratio, then audits failed headroom results. The audit stdout also prints headroom_rejections=..., pair_evidence_quality=..., pair_trigger_reasons=..., pair_evidence_hypotheses=..., and pair_evidence_hypothesis_triggers=... handoff rows, plus pair_trigger_historical_aliases=... when archived evidence includes legacy trigger aliases and pair_evidence_hypothesis_trigger_gaps=... when documented hypotheses have not yet propagated into trigger reasons, with the rejected-fixture coverage counts plus actual minimum pair margin, maximum pair/solo wall ratio, and canonical trigger reason coverage plus row-match status. The compact evidence row count must match the frontier evidence count, checks.frontier_stdout records summary, aggregate, final-verdict, expected, printed score-row, trigger-visible row, and hypothesis-trigger-visible row counts, checks.headroom_rejections records child verdict plus unrecorded/unsupported counts, checks.pair_evidence_quality records the same quality thresholds from the compact rows, checks.pair_trigger_reasons records canonical/historical-alias/exposed/total trigger-reason row counts, fixture-level historical alias details, summary count, and row-match status, checks.pair_evidence_hypotheses records documented/total pair-evidence hypothesis row counts, and checks.pair_evidence_hypothesis_triggers records whether documented hypotheses also appear as spec.solo_headroom_hypothesis trigger reasons plus fixture-level gap details so incomplete or low-quality local score artifacts cannot inflate the claim. Add --require-hypothesis-trigger to turn those hypothesis-trigger gaps from archived-evidence WARN rows into release-blocking FAIL rows for newly regenerated pair evidence.

npx devlyn-cli benchmark audit --require-hypothesis-trigger --out-dir /tmp/devlyn-benchmark-audit-strict

Historical trigger aliases are only reported for archived artifact review; new current pair-evidence gates fail historical-only or unknown trigger reasons and require at least one canonical pair_trigger.reasons entry. benchmark audit-headroom fails if an active failed headroom fixture is missing from both rejected registry and passing pair evidence. Headroom runs use the current claim gate: bare <= 60, solo_claude <= 80, and the default 5-point bare/solo_claude headroom margins before spending a pair arm. Add --dry-run to either score runner to validate args, fixture ids, minimum fixture count, and the replay command without running arms or judges. Dry-runs and lint prove wiring only; real score claims must cite the run id and fixture ids.

Optional Power-User Skills

Two creative companion skills live in optional-skills/ — install them via the interactive installer when you need them.

| Command | Use When | |---|---| | /devlyn:design-system | Extract exact design tokens (colors, type scale, spacing) from a chosen UI style | | /devlyn:team-design-ui | Multi-perspective design team generates 5 distinct UI style explorations |

Earlier versions of devlyn-cli shipped 16+ skills (auto-resolve / preflight / evaluate / review / team-review / clean / update-docs / browser-validate / product-spec / feature-spec / recommend-features / discover-product / design-ui / implement-ui). Most were consolidated into /devlyn:resolve (which folds verification, review, and cleanup into its phases) plus /devlyn:ideate (which absorbs the planning surfaces) in the iter-0034 Phase 4 cutover (2026-05-04). /devlyn:design-ui is now installed as a required creative UI surface. Upgrades automatically remove the legacy skill directories from ~/.claude/skills/.

Auto-Activated Skills

These activate automatically — no commands needed. They shape how Claude thinks during relevant tasks.

| Skill | Activates During | |---|---| | root-cause-analysis | Debugging — enforces 5 Whys, evidence standards | | code-review-standards | Reviews — severity framework, approval criteria | | ui-implementation-standards | UI work — design fidelity, accessibility, responsiveness | | code-health-standards | Maintenance — dead code prevention, complexity thresholds |

Optional Add-ons

Selected during install. Run npx devlyn-cli again to add more.

| Skill | Description | |---|---| | asset-creator | AI pixel art game asset pipeline — generate, chroma-key, catalog | | cloudflare-nextjs-setup | Cloudflare Workers + Next.js with OpenNext | | generate-skill | Create Claude Code skills following Anthropic best practices | | prompt-engineering | Claude 4 prompt optimization | | better-auth-setup | Better Auth + Hono + Drizzle + PostgreSQL | | pyx-scan | Check if an AI agent skill is safe before installing | | dokkit | Document template filling for DOCX/HWPX | | devlyn:pencil-pull | Pull Pencil designs into code | | devlyn:pencil-push | Push codebase UI to Pencil canvas | | devlyn:reap | Safely reap orphaned MCP / codex / Superset child processes | | devlyn:design-system | Extract design tokens from a chosen UI style for exact reproduction | | devlyn:team-design-ui | 5 distinct UI style explorations from a full design team |

| Pack | Description | |---|---| | vercel-labs/agent-skills | React, Next.js, React Native best practices | | supabase/agent-skills | Supabase integration patterns | | coreyhaines31/marketingskills | Marketing automation and content skills | | anthropics/skills | Official Anthropic skill-creator with eval framework | | Leonxlnx/taste-skill | Premium frontend design skills |

| Server | Description | |---|---| | playwright | Playwright MCP — powers /devlyn:resolve BUILD_GATE browser tier (Chrome MCP → Playwright → curl fallback) |

--engine auto/codex and conditional VERIFY pair mode use the local codex CLI binary, not MCP. Install from https://platform.openai.com/docs/codex, run the current Codex auth/login flow, verify codex --version, then rerun.

Want to add a pack? Open a PR adding it to the OPTIONAL_ADDONS array in bin/devlyn.js.

Requirements

• Node.js 18+
• Claude Code installed and configured

Contributing

• Add a skill — directory in config/skills/ with SKILL.md
• Add optional skill — add to optional-skills/ and OPTIONAL_ADDONS in bin/devlyn.js
• Suggest a pack — PR to the pack list

Star History

License

MIT — Nocodecat @ Donut Studio