--- id: 901363 card_url: "https://mdrss.com/llm-engineering/training-and-fine-tuning/901363" permalink_url: "https://mdrss.com/m/901363" thread_url: "https://mdrss.com/s/llm-engineering" markdown_url: "https://mdrss.com/llm-engineering/training-and-fine-tuning/901363/901363.md" title: "Eval Harness First" annotation: "The Phase 0 gate for the whole plugin: finetuning-method-selection and every downstream skill assume this harness exists before a training config gets written. The harness is not a run-end side artifact — it is the data-curation engine. The same labeled traces that build the go. Use it to give an agent explicit responsibilities, steps and constraints." state: published thread: llm-engineering domain: llm-engineering category: training-and-fine-tuning type: guide tags: ["llm-ml-engineering", "training-fine-tuning", "harness", "eval", "first", "phase", "gate", "training", "llm-engineering", "collider-club"] ontology_terms: ["concept:training-fine-tuning", "org:collider-club"] relation_terms: [] license: "MIT" version: 1 snapshot_at: "2026-08-04T16:17:00.000Z" source_url: "https://github.com/wshobson/agents" source_kind: "collider-club-curated" platform_scam_risk: 5 platform_evidence_score: 100 evidence_urls: - "https://github.com/wshobson/agents" - "https://raw.githubusercontent.com/wshobson/agents/c4b82b0ad771190355eb8e204b1329732a18449a/plugins/llm-finetuning/skills/eval-harness-first/SKILL.md" - "https://collider.club" - "https://opensource.org/licenses/MIT" --- # Eval Harness First > The Phase 0 gate for the whole plugin: finetuning-method-selection and every downstream skill assume this harness exists before a training config gets written. The harness is not a run-end side artifact — it is the data-curation engine. The same labeled traces that build the go. Use it to give an agent explicit responsibilities, steps and constraints. > Editorial note: curated source snapshot published by [Collider.club](https://collider.club) under the MIT License. Source attribution is preserved in the front matter. ## Original source metadata ```yaml name: eval-harness-first description: Build the evaluation harness that gates every fine-tuning run — golden sets, per-failure-mode graders, judge calibration, and base-model baselines. Use when starting a fine-tuning effort, when converting traces into an eval set, or when calibrating a judge against human labels. ``` ## Source snapshot # Eval Harness First The Phase 0 gate for the whole plugin: `finetuning-method-selection` and every downstream skill assume this harness exists before a training config gets written. The harness is not a run-end side artifact — it is the data-curation engine. The same labeled traces that build the goldens feed training data, minus an explicit holdout. **Input:** production/agent traces if they exist, or a task spec if they don't, plus labelers willing to grade ≥100 examples. **Output format:** the `eval/` directory below — goldens, graders, drift suite, and the base-model baseline that later phases gate on. ## The Gate No eval harness, no fine-tune. Skip to a training config and there is nothing to measure against, nothing to catch regressions, and no labeled data to train on. The flywheel: 1. **Collect traces** — production/agent spans, or synthetic tasks if none exist yet. 2. **Error analysis** — open coding on ≥100 traces, axial coding into 4–8 failure buckets. 3. **One grader per bucket** — deterministic first; calibrated LLM-judge only for genuinely subjective criteria. 4. **Prioritize** by frequency × severity × value. 5. **The labeled traces feed dataset curation, minus an explicit holdout.** Every `eval/goldens.jsonl` ID stays excluded from training data by ID. 6. **Train.** 7. **Re-run the same harness** on the checkpoint — not a different, looser one. 8. **Drift detection feeds back to step 2** — new production failure modes re-open error analysis. Steps 2–4 build the harness; steps 5–8 are why it must exist first — it is both the training data source and the checkpoint's exit gate. ## Building Goldens - **From traces, when they exist:** run error analysis — open coding on ≥100 real traces (read them, tag failures in your own words, no fixed taxonomy yet), then axial coding to collapse those tags into 4–8 named failure buckets. Fewer than 4 means the coding pass was too shallow; more than 8 means buckets need merging. **Exception:** single-failure-surface tasks (e.g. strict-schema extraction) may land at 1–2 buckets with per-field sub-metrics inside one grader — don't invent artificial splits with no evidence behind them. - **Synthetic, when traces don't exist yet:** dimension-based generation — enumerate the axes that matter (task type, difficulty, edge case, persona) and sample the cross-product; free- generated prompts cluster around whatever's easiest to write. - **Goldens are versioned like code** — commit `eval/goldens.jsonl`, diff it in review, tag it per release. It doubles as the CI regression suite. ## Graders One grader per failure bucket from error analysis — not one for the whole eval set. A single blended score hides which bucket regressed. - **Deterministic first.** Regex, schema validation, or execution checks are cheaper, reproducible, and need no calibration. - **LLM-judge only for genuinely subjective criteria** — tone, faithfulness, "which response is better" — where no deterministic check can express it. - **Binary pass/fail over Likert.** A 1–5 or 1–10 scale is noisier to calibrate and harder to apply consistently; collapse to pass/fail. - **Drift-suite MMLU-style scoring: prefer logprob over generate-and-extract** — a tight token budget makes generate-and-extract parse-brittle for models that preamble, conflating format compliance with the knowledge being measured. Templates for all four grader shapes and this scoring note: `references/grader-templates.md`. ## Judge Calibration Is a Prerequisite Any bucket routed to an LLM-judge needs calibration before its verdicts count for anything beyond exploration — a hard prerequisite, not a nice-to-have. **N/A when no bucket routes to a judge** — an all-deterministic harness has nothing to calibrate; state that rather than leaving this section unaddressed. - Label ≥100 items, split **train**/**dev**/**sealed test** (report once, no re-touching after). - Report **TPR and TNR**, not one blended accuracy number — a judge can hit 90% by always saying "pass" on a skewed set. - **Pin the judge to a fixed model snapshot** and recalibrate on judge-model change, quarterly regardless. - **The judge must come from a different model family than the model under test.** - A judge that misses the agreed TPR/TNR bar ships **advisory-only** — flags for human review, never gates a promotion. Full protocol, bias correction, and recalibration checklist: `references/judge-calibration.md`. ## The Baseline Before Phase 1 (method selection) starts, run the full harness — goldens plus the capability-drift suite — against the unmodified base model. This is the number every later checkpoint gets compared against. `eval/baseline-.json` is the gate token. No baseline file, no comparison basis for `checkpoint-promotion` — a checkpoint that "looks better" against nothing measured isn't a finding. ## Directory Contract ``` eval/ ├── goldens.jsonl # labeled traces + synthetic goldens, versioned ├── graders/ # one module per failure bucket │ ├── schema_compliance.py │ ├── exact_match.py │ └── rubric_judge.py ├── drift-suite.yaml # frozen benchmarks + 200-500 domain-adjacent items └── baseline-.json # gate token: harness + drift suite vs the base model runs/ └── / └── results.json # per-run harness output, one per checkpoint ``` `eval/` persists across runs and lives outside `runs/` — the fixed measuring stick, not a run artifact. `runs/` is disposable; `eval/` is not. Never let a run script write into `eval/`. **Canonical location:** every per-trace `results.json` — the Phase 0 baseline included — lives at `runs//results.json`, never under `eval/runs/...`; an instruction requesting the latter is wrong, not this contract. ### Phase 0 Exit Checklist Before `finetuning-method-selection`, confirm: 1. ≥100 traces open-coded; 4–8 failure buckets (N/A floor for synthetic goldens on a single-failure- surface task — see the Building Goldens exception; bucket count then comes from post-baseline error analysis instead). 2. `eval/goldens.jsonl` committed and versioned. 3. One grader per bucket, deterministic first. 4. Judges calibrated — TPR/TNR, snapshot pinned, different family (**N/A when no bucket routes to an LLM-judge**; state that explicitly). 5. `eval/drift-suite.yaml` frozen. 6. `eval/baseline-.json` written. Missing any of the six (or its stated N/A)? Not Phase 0 complete — `/finetune` checks the baseline file before a run. ## Related Skills General-purpose evaluation guidance (dashboards, A/B testing, non-fine-tuning harnesses) lives in the `llm-application-dev` plugin's `llm-evaluation` skill — this skill covers only the fine-tuning coupling: goldens that double as training data, and the baseline that gates a checkpoint. - `finetuning-method-selection` — routes here first. - `dataset-curation` — formats these traces into training rows. - `trace-to-training-data` — turns graded traces into training examples. - `checkpoint-promotion` — consumes `baseline-.json`, re-runs this harness on each candidate checkpoint. ## References - `references/grader-templates.md` — runnable grader examples per shape, plus a `drift-suite.yaml` example and MMLU logprob-scoring note. - `references/judge-calibration.md` — the calibration protocol, including the all- deterministic N/A path. --- ## About Collider.club This card belongs to the curated knowledge base of **[Collider.club](https://collider.club)** — a closed business club for entrepreneurs, engineers, investors and domain experts building projects for international markets. Members work across DeFi, AI/ML, FinTech, Web3, banking, hardware and venture capital, and the club runs closed sessions on high-margin niches with anonymous speakers. - Club: - Collection: Collider.club curated card library (`mdrss-card/v2`) - Maintainer: Collider.club editorial team ## License MIT License — Copyright (c) 2026 Collider.club. Full text: [LICENSE](../../LICENSE) ·