# Harness Engineering > Harness engineering for Harness Kit primitives: skills, shared doctrine, provider roster, harness configs, gates, evals, bootstrap, and sync logic. Use for "improve the harness", "harness engineering", "bootstrap is wrong", "AGENTS.md is stale", "skill health", "skill usage", "undertriggering skill", "description tax", "eval skill", "sync primitives", "roster defaults", "preferred stack", "stack defaults", "hosting defaults", "CI defaults", "observability defaults", "release defaults", "design system defaults", "storage defaults", "agent substrate defaults", "one core many faces", "API CLI MCP SDK skill template", "factory product template", "generate repo-local skill", "bespoke skill subset", "domain agent skill". Trigger: /harness-engineering, /harness, /skill. - Skill: `phrazzld/harness-engineering` (Agent Skill, multi-file: 41 files) - Install (CLI): `npx skillmds@latest add phrazzld/harness-engineering` - Raw SKILL.md: https://api.skillmd.com/api/skills/phrazzld/harness-engineering/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Design & Media - Author: phrazzld (https://skillmd.com/u/phrazzld) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/phrazzld/harness-engineering --- # /harness-engineering Engineer the harness. Keep it thin. ## Route | Need | Load | |---|---| | create skill or prompt | `references/mode-create.md` | | eval skill | `references/mode-eval.md` | | lint skill | `references/mode-lint.md` | | apply skill-design lessons | `references/skill-design-principles.md` | | clean skill catalog | `references/mode-audit.md` + `harness-kit-checks telemetry` | | convert agent/skill | `references/mode-convert.md` | | sync externals | `references/mode-sync.md` | | engineer doctrine/gates/hooks | `references/mode-engineer.md` | | measure skill usage/health/staleness | `references/mode-audit.md` | | current model/provider/harness facts | the roster skill's `references/model-provider-harness-index.md` | | open-model defaults | `references/open-model-roster.md` | | preferred stack / infrastructure defaults | `references/preferred-stack.md` | | factory app capability routing | `../factory-apps/SKILL.md` | | one core / many faces product template | `references/one-core-many-faces.md` + `templates/one-core-many-faces/` | | generate a focused repo-local skill for a domain agent | `references/repo-local-skill-generation.md` + `templates/repo-local-skill/` | | public-surface "works" critique | `../../harnesses/shared/references/works-critique.md` | | model-native product boundary | `../../harnesses/shared/references/model-native-product-primitives.md` | | loop readiness / Mode B handoff | `../../harnesses/shared/references/loop-readiness.md` | | verification system first | `../../harnesses/shared/references/verification-system-first.md` | | delete-first simplification lens | `../../harnesses/shared/references/delete-first.md` | | Ponytail anti-overengineering ladder | `../.external/dietrich-ponytail/SKILL.md` | Repo-local skills for consumer repos (bespoke QA drivers, deploy runbooks, persona probes) are written directly into that repo's `.agents/skills/` with its real routes and commands; this skill owns the craft either way. Process, provenance header, and eval-stub shape: `references/repo-local-skill-generation.md` + `templates/repo-local-skill/`. For a repo's verification skill, interview the operator first: the manual checks they run after the agent responds and before merge are the spec — encode each check that has a tool. Turning a proven session pattern into a first-party primitive starts at the primitive test below — most patterns are prompts, not skills. ## Contract - Fix root cause in the highest-leverage layer: type/test/hook/gate/skill/ AGENTS, in that order. - Prefer deletion. Harness prose is context tax. - Use Ponytail before adding or expanding primitives, provider layers, harness-specific accelerators, gates, wrappers, or skill prose. The lazy viable path has to lose on evidence before a larger harness mechanism earns its place. - Cross-harness first means filesystem + `SKILL.md` portability. Prefer smoke-tested open-model peer lanes through Pi, Goose, and OpenCode on OpenRouter; keep Claude, Antigravity, Cursor, and Grok conditional unless their specific surface answers the task. - Skills stay self-contained: scripts/libs/references under the skill; state roots from invoking repo. - Code outside a skill serves only Harness Kit source-repo maintenance, generated artifacts, bootstrap/install, or harness configuration. It is not a place for skill behavior. - Treat a skill as a folder, not a markdown file. Use scripts, references, examples, templates, assets, evals, or append-only data when prose would make the agent reconstruct repeatable work. - Model/provider/harness selection facts live in the roster skill (`skills/roster/references/model-provider-harness-index.md`). Keep that file factual: model ids, context, price, latency/smoke evidence, tool support, benchmark sources, deprecations, and freshness. Do not encode role-fit policy there; the lead agent composes task-specific teams from current evidence. - Harness Kit source skills live in `skills/`; repo-local `.agents/skills/` and harness-specific skill bridge dirs are `/seed` output for consumer repos. - Generated/root `AGENTS.md` is a router, not a manual. Keep non-obvious facts only. - System bootstrap exposes the full first-party skill catalog; repo-local vendoring is exceptional and must earn its complexity. - Provider CLIs are tools. Do not wrap them in semantic orchestration unless a shaped ticket explicitly asks. - Harness-specific accelerators (e.g. orchestration-workflow templates) may ride inside a skill folder as assets the prose names as optional — a harness without the feature must lose nothing by ignoring them. Build one only after telemetry shows the pattern recurring; never pre-author. ## Delegation Judgment delegate on judgment per the shared Roster contract: native subagents by default; add cross-model critics, roster providers, or sprite lanes (`/sprites`) only when they answer a distinct question. See `harnesses/shared/AGENTS.md` (Roster). Local lane guidance: Use lanes for doctrine critique, runtime compatibility, gate design, and regression risk. Do not treat a missing repo-local roster as a waiver; use the resolver-backed probe. ## Primitive Test Before creating or growing anything, classify it (2026-06 audit, backlog 103): - **Local prompt** — "is this just what the operator would retype to a strong model?" Keep it in chat, local scratch, or a skill template only when a skill truly needs reusable wording. Do not add a repo-level prompt layer. If the operator expects Codex app slash or `$` discovery, use a skill instead. - **Skill** — "does this change what a frontier model does, for the better, repeatedly?" Judgment + context the model can't derive. - **Doctrine line** — "worth paying for in every session?" Goes in AGENTS.md, not a folder. - **Mode B** — event-triggered (on PR-ready, on production error, on schedule)? It belongs in the event plane (bitterblossom), not this harness. This repo is the ad-hoc operator layer plus the shared disk contracts. Load `harnesses/shared/references/loop-readiness.md` before proposing any unattended loop. History: slash commands were collapsed into skills when skills arrived, so saved prompts masqueraded as skills and the catalog tripled. Do not recreate that. Counter-history: Codex app discovery is skill-shaped, so high-frequency operator commands that must appear in the app are skills even when their body is lightweight. ## Quality Bar - `SKILL.md` encodes judgment, not a procedure the model already knows. - Frontmatter descriptions are model trigger classifiers, not human summaries: include explicit `Use when:` phrases and `Trigger:` aliases. - Instruction prose is compression, not literature. Sacrifice grammar before clarity; keep terse imperatives, named failure modes, and concrete oracles. - Put long mode detail in `references/`; keep the entry file short. - Build gotchas from repeated agent failures. If a gotcha can be asserted by a script, hook, or eval, codify it there and point the skill at the artifact. - Ad-hoc roster lanes beat static project subagents unless tool permissions must be isolated. - New mechanisms include a verification system: gate, eval, benchmark, QA path, smoke path, or probe that can fail for the real error. - Every run ends clean: no untracked or modified files. ## Post-Sync Acceptance After changing skills, shared doctrine, generated docs, bootstrap, roster, or harness projections, prove the output is repo-fit, not merely structurally valid. ```markdown ## Acceptance Evidence - Live repo evidence read: source skill, shared doctrine, generated docs, bootstrap output, roster, or harness projection inspected. - Acceptance source: backlog oracle, skill contract, generated index/docs contract, bootstrap contract, or explicit absence. - Evidence that proves it: command output, diff, generated artifact, bootstrap transcript, or gate output. - Exact command/path/route exercised: check, generator, bootstrap, smoke path, projection path, or route run. - Oracle / acceptance artifact hash: sha256 digest for any fixture, generated artifact, transcript, or contract used as the oracle, or state that no artifact-backed oracle exists. - Contract-change acknowledgment: reason when the change alters an acceptance contract, generated source, or assertion surface, or state that no contract changed. - Repo-fit check: source/generator/projection agree; no stale generated docs, wrong skill root, stale command, or copied bridge remains. - Structural gate: `check --repo .` result, or the specific sub-gate exercised. - Residual risk: skipped harness, external dependency, or none with reason. ``` ## Gotchas - Phase prose is not judgment. Frontier models know the SDLC; a skill that restates implement/refactor/review steps is railroading (Anthropic's own top skill lesson: don't state the obvious, avoid railroading). Encode the bespoke part — oracles, repo facts, taste — or nothing. - Process bureaucracy trains checkbox compliance, not quality. Multi-field completion gates, oracle hashes, and learning-packet ceremonies get filled in plausibly by strong models. Verification is tests, CI, and driving the live surface. - Evals, benchmarks, and QA are verification systems only when they have a driver, grader, evidence packet, and cadence. A directory, prompt, or transcript with no falsifier is not proof. - Deterministic scaffold is the historical failure mode here: agents unsure of harness engineering fall back to Rust/scripts that enforce prose. Every gate must answer "what real failure did you catch in the last 90 days?" — no answer, delete it. - Check telemetry before adding or keeping a skill. The 2026-06 audit found ~15 of 36 skills unused; usage is a power law. Low usage with high value-when-used is fine (say so); low usage with no story is deletion. - A new frontier model release silently converts some skill prose from judgment into railroading: instructions tuned for the last model anchor the new one to stale patterns. After a major model ships, re-audit skill and doctrine prose; prefer deleting an instruction over updating it. - Name harness features by capability, not vendor. "Use the harness's large-scale orchestration feature when it has one" degrades gracefully across harnesses; "use dynamic workflows" confuses every harness that lacks them. - Meta-work ratio: if this repo's commit rate rivals the product repos', the flywheel is feeding itself. - Stale AGENTS prose is worse than missing prose. - Duplicated repo-local skill copies are usually stale context unless a repo needs checked-in vendored harness state. - Generated catalog/docs drift means the source skill changed but the harness projection did not. - Unsupported invocation hooks mean usage telemetry is structurally shaped but not empirically proven for that harness. - Structural eval trees are not semantic proof; objective graders must assert behavior or carry an explicit waiver. - Helper scripts that are not wired into a gate become optional folklore. - Regexes over agent prose are usually the wrong boundary. - If a rule matters, enforce it outside prose. ## Verification Run `cargo run --locked -p harness-kit-checks -- check --repo .` after changing harness primitives, gates, roster, bootstrap, or sync logic. For bootstrap changes, also re-run bootstrap and confirm installed skills/configs match the source tree and retired prompt/example links are pruned.