| name | eval-compare-backends |
| description | Compare eforge eval runs of the same scenario across two or more backends. Reads eforge.log, result.json, and workspace artifacts to judge decision quality stage-by-stage — pipeline composer, planner, builder, tester, reviewer, review-fixer, evaluator — and writes a ranked analysis to the results directory. Use when the user asks to compare backends, rank backends, analyze which backend made better decisions, or review a specific eval run. |
eval-compare-backends
Qualitative, judgment-driven comparison of eforge eval runs across backends. lib/compare.ts already produces numeric rankings (comparison.json); this skill answers the harder question: which backend made better decisions?
Invocation
- Slash:
/eval-compare-backends — defaults to latest run, all scenario groups with ≥2 backends.
- Slash with args:
/eval-compare-backends <timestamp> [scenario-id] — e.g. /eval-compare-backends 2026-04-14T16-19-24 todo-api-errand-health-check.
- Natural language: any request to compare backends, rank backends, judge decision quality on an eval run.
If the user names a specific run, use it. Otherwise find the most recent results/YYYY-MM-DDTHH-MM-SS/ directory.
Discovery
- List
results/ entries matching the timestamp pattern, newest first.
- Within the chosen run, list subdirectories matching
<scenario-id>--<backend-name>.
- Group by
<scenario-id>. Skip groups with fewer than 2 backends.
- If the user passed a scenario ID, filter to that group.
Read order — logs are the decision record, metrics are the numbers
Read per backend, in this order:
eforge.log — authoritative for what each agent decided. Pipeline-composer JSON output, planner's chosen profile, which build agents actually ran, review issues raised, evaluator verdicts. Cite by line number when possible.result.json — authoritative for tokens, cost, duration, per-agent aggregates. Also contains expectations check results and the backend.profile so you know what model/backend was configured. Also inspect metrics.models — backends often mix models across agents (e.g. opus for planner/builder, sonnet for prd-validator). To find which agent used which model, query the monitor DB directly: SELECT agent, data FROM events WHERE type='agent:result' AND run_id IN (...) and read each row's result.modelUsage keys. Worth calling out when a cheaper model is routed to low-stakes stages — that's a deliberate design choice, not an accident.result.json.quality.absolute (if present) — LLM-as-judge absolute rubric over the PRD + final git diff. Has per-dimension scores (prdAdherence, codeQuality, testQuality, changeDiscipline) on a 1-5 scale plus overall.weighted. The judge is a separate one-shot Opus call with tools disabled (see lib/score-quality.ts); treat it as an independent cross-check on the artifact, not a substitute for log reading. Inputs are snapshotted at <scenarioDir>/quality/{prd.md,diff.patch} — read those if a score looks suspicious.comparison.json (if present) — numeric rankings across cost/tokens/duration/cache/pass-fail, plus a quality dimension under groups[].dimensions.quality (pairwise LLM-as-judge over the same PRD + diff snapshots). Cite directly for the quantitative dimensions; don't recompute.validate-*.log — whether install/type-check/test actually passed in the workspace.workspace-path.txt → git log --stat or git show in that workspace — use only when scope creep is suspected (e.g. a doc-updater ran). Look for files touched that the PRD didn't ask for.
Metrics aggregator caveat — check this early
Sanity-check before trusting any numbers. If result.json's metrics.agents contains only formatter (or is otherwise missing stages the log clearly shows ran), the aggregator bug was present when that run was built. The log will show planner/builder/tester/etc. running, but result.json will undercount tokens and cost by ~25× or more.
When detected:
- Flag it prominently in the
Notes section of the report, including the true numbers vs. what result.json says.
- Reaggregate by calling
buildResult from lib/build-result.ts against the current DB, or by querying the monitor DB directly (see read step 2 above for the query).
- Treat
comparison.json as also contaminated — its rankings inherit the bad per-backend numbers.
The bug was fixed in lib/build-result.ts:resolveRunIds — runs built after that fix should have all stages represented.
Comparison dimensions
Judge each dimension per backend. Declare a winner (or tie) with a one-line reason citing the log:
| Dimension | What to look for |
|---|
| Pipeline composer | Scope choice (errand/excursion/expedition), pipeline shape, review strictness. Is it proportional to the PRD? |
| Planner | Did it respect the scenario's expect.mode? Did it downgrade/upgrade the composer's pipeline when warranted? Did it decompose sensibly? |
| Builder | Correctness, scope discipline, whether it installed/touched only what the plan required. |
| Tester | Coverage of acceptance criteria, genuine bug catches vs rubber-stamping. |
| Reviewer | Real-bug-to-speculation ratio. Did flagged issues matter, or were they style hypotheticals? |
| Review-fixer | Applied fixes discriminately or yes-manned the reviewer? |
| Evaluator | Did it catch bad fixes? Accept real ones? |
| Doc discipline | See Doc discipline section below. Applies to every backend, not just ones that ran a doc-updater. |
| Scope discipline | Non-doc files touched vs. files the PRD asked for. Run git log --stat in the workspace if unsure. |
| Final artifact | Did validation pass? Is the artifact equivalent across backends, or is one genuinely better? |
| Quality (LLM-as-judge) | Cite result.json.quality.absolute.overall.weighted per backend and the pairwise comparison.json.groups[].dimensions.quality ranking. Use as an independent cross-check, not the final word — investigate the lowest-scoring dimension before accepting the verdict. |
Doc discipline
For each backend, enumerate every write/edit under docs/, README*, CHANGELOG*, or any other doc-looking path. Query the monitor DB for agent:tool_use events across all agents (not just doc-updater) — the builder can touch docs too:
SELECT agent, data FROM events
WHERE type='agent:tool_use' AND run_id IN (...)
Filter tool inputs (Write, Edit, file_path; Bash commands with doc paths) for paths under documentation locations.
Classify each touched path:
- PRD source — matches any
scenarios.yaml prd: field, or is under eforge/queue/. Touching a PRD source is an anti-pattern. PRDs are historical inputs, not living docs. Flag red, even if the backend touched a different scenario's PRD (compounds the anti-pattern).
- Project doc — README, API reference, architecture notes, changelogs, or anything under
docs/ that isn't a PRD source. Judge per-file:
- Code change affects the surface this doc describes → appropriate update.
- Code change orthogonal → over-reach.
- Missed update — project docs the fixture already has that arguably should have changed given the code change, but didn't. Requires reading the fixture's docs to detect. Apply to every backend (including ones that never ran a doc-updater stage).
Score the backend on: PRD touches (any = red), project-doc touches (appropriateness per path), missed updates.
Fixture note: if the fixture has no project documentation (only PRD sources), record this as a fixture observation separately from the backend scoring. A backend that ran a doc-updater stage against a doc-less fixture isn't purely at fault — the pipeline shouldn't have composed doc-update for that fixture, or the fixture is under-specified. Call it out so the fixture gap is visible.
Not every dimension applies to every run — skip stages that didn't execute for any backend.
Ranking (N-backend)
For each dimension, rank all backends (ties allowed). For the overall verdict:
- Weight decision quality over raw cost. A backend that costs 2× but makes the right scope call is usually the better choice.
- Weight scope discipline heavily. Unrelated file edits are a red flag even if the final artifact passes.
- Equivalent output ≠ equivalent decisions. Two backends that produce identical
/health endpoints may still rank very differently if one got there via a bloated pipeline.
- Per-stage self-correction (e.g. evaluator catching a bad fixer) is a positive signal but rescuing wasted work < avoiding it.
- A backend that skips a stage by good judgment outranks one that runs the stage and then rejects its output.
Produce an ordered ranking with a clear #1, plus callouts for backends that shine on a specific dimension even if not overall #1.
Output
Two artifacts:
1. Chat response
Concise. For each scenario group:
- A per-dimension scorecard table (rows = dimensions, columns = backends, cells = rank or ✓/✗/~).
- 2-4 sentences of overall verdict naming the winner and the decisive dimension(s).
- Key surprises or caveats (metrics bug, unexpected model choice, validation gap).
2. Markdown report
Write to results/<timestamp>/backend-analysis.md (one file per run, covering all scenario groups in that run). Overwrite if it exists.
Structure:
# Backend Analysis — <timestamp>
Generated: <ISO timestamp>
Scenarios analyzed: <N>
## <scenario-id>
**Backends:** <backend-a>, <backend-b>, ...
**Ranking:** 1. <winner>, 2. <runner-up>, ...
### Scorecard
| Dimension | <backend-a> | <backend-b> | ... |
|---|---|---|---|
| Pipeline composer | ... | ... | ... |
| Planner | ... | ... | ... |
| ...
### Stage-by-stage
#### Pipeline composer
<backend-a>: <what it chose and why, with log line cite>
<backend-b>: ...
**Winner:** <name> — <one sentence>
#### Planner
...
### Verdict
<2-4 sentences. Name the winner, the decisive dimension, and any meaningful
caveats. Distinguish decision quality from output quality.>
### Notes
- <metrics bug flag if applicable>
- <unexpected findings>
Cite eforge.log:<line> inline for specific decisions. Include the backend.profile (backend kind, models) near the top of each section so the reader knows what was actually tested. When a backend uses multiple models, list which agent used which — e.g. "claude-opus-4-6 for planner/builder/tester, claude-sonnet-4-6 for prd-validator". Mixed-model routing is a deliberate design choice worth surfacing.
Guardrails
- Don't declare a winner on metrics alone.
comparison.json already ranks those.
- Don't invent stages. If a stage didn't run for a backend, say so — often that is the interesting decision.
- Cite line numbers. Vague claims like "the planner did X" without a cite make the report unverifiable.
- When metrics and logs disagree, log wins and flag it.
- Don't trust validation pass alone when judge quality disagrees. If
validate-*.log is green but quality.absolute.overall.weighted < 3 (or any single dimension is 1-2), investigate before declaring the artifact correct. Validation can pass vacuously when no source changes were made — git log --stat in the workspace settles it. The judge's diff snapshot at <scenarioDir>/quality/diff.patch is the same input the judge saw; read it directly when scores look off.
- Don't guess at workspace state. If you need to know what files changed, actually read
workspace-path.txt and run git log --stat or git show in the workspace.
- Keep it short. A 4-backend comparison should still fit in a reviewable page or two. Resist the urge to re-summarize the PRD or the eforge pipeline generically.
