By name: running-with-without-evals description: Use when producing or refreshing a "with vs without Systematic" demo, an A/B plugin evaluation, or any recorded-session comparison of OpenCode behavior with and without a plugin loaded — for a public page, a credibility artifact, or internal validation.
Running With/Without Evals
Overview
A with/without eval captures real opencode run transcripts on the same task, once with a plugin loaded and once without, to show what the plugin actually changes. The output is recorded sessions, not a benchmark.
Core principle: the result is only worth publishing if it would survive a hostile reader who has the transcripts. That means pre-registering the bar before you run, keeping a clean baseline, including the control that could disprove your thesis, and conceding what the baseline already does well.
The reusable harness lives at tests/manual/with-without-eval/run-arm.sh. Reuse it; don't reinvent the isolation.
When to use
- Building or refreshing the
with-without-systematicdemo page - Validating that a plugin/skill change actually moves model behavior
- Producing a credibility artifact for public promotion
When NOT to use
- You need statistical claims — this is n=1–3 recorded sessions, not a benchmark. Don't dress it up as one.
- The task is trivial (the baseline will look fine and the eval proves nothing)
The method
- Pre-register first. Write the task, the models, and the publishable-delta bar to a
PRE-REGISTRATION*.mdBEFORE any run. State the no-ship condition (if the bar isn't cleared, ship an honest decision guide, not a staged win). Committing this first is what lets you claim the result wasn't retrofitted. - Run each arm via
run-arm.sh <baseline|treatment> <model> <prompt-file> <out-dir> [seed-dir]. Baseline =--pure+ empty plugin array; treatment = plugin loaded. Use a paid model — free models rate-limit and the failure masquerades as empty output. - Verify the baseline is clean and the treatment loaded — the script checks
systematic_skillis absent (baseline) / present (treatment). A contaminated baseline is a dishonest demo. - Add the controls that matter (see below) before drawing conclusions.
- Have Oracle review the methodology and the drafted page before publishing. Council for the design if the matrix is non-trivial.
Isolation recipe (the part that bites)
Redirect only XDG_CONFIG_HOME to drop the user's global config and its MCP servers for a vanilla baseline. Do NOT redirect XDG_DATA_HOME (holds auth.json — the paid model won't authenticate) or XDG_CACHE_HOME (holds the model catalog — ProviderModelNotFoundError). OPENCODE_CONFIG_DIR=<empty temp> skips the project-level user config; OPENCODE_CONFIG_CONTENT sets the per-arm plugin array. This is the minimum isolation that works — heavier isolation breaks auth and model resolution.
Required controls
- Prompt-parity control. Run a no-plugin arm whose prompt also says "brainstorm, plan, implement, review." This separates "asking for review" from "the plugin." If the plugin's only effect is reproducible by a better prompt, the honest thesis is narrower — say so. This control is non-negotiable; it is the first thing a skeptic will ask for.
- Variance on the headline cell. Run the bare baseline n=3. If it misses the key risk 3/3, that's a real signal. Publish the median; never cherry-pick from k runs.
- Seed the workspace for tasks that assume existing code. A task like "add OAuth to my Express app" stalls in an empty temp dir — the model asks for files. Pass a
seed-dirwith a realistic pre-existing app. The seed must NOT hint at the task's solution (that contaminates the baseline upward).
Honest framing (non-negotiable)
- Frame as "recorded sessions," not "evaluation" or "benchmark" — the word benchmark invites scrutiny n=1 can't survive.
- Concede baseline competence up front. Modern models write solid first drafts. Claiming otherwise loses the technical reader in paragraph one. The claim is the process gap (review happens at all), not a quality gap.
- Feature the prompt-parity control prominently, including in any summary table. Burying it is the difference between a credible artifact and marketing sludge.
- State exact n per condition and disclose that the treatment prompt differs (it invokes the workflow — that's how the plugin is used).
- Real transcripts only. If a result underwhelms, fix the product or narrow the framing — never edit the transcript.
Common mistakes
| Mistake | Fix |
|---|---|
| Empty workspace for a task that assumes existing code | Seed the workspace; verify the model has files to modify |
| Redirecting all XDG dirs for "clean" isolation | Only XDG_CONFIG_HOME; the others hold auth + model catalog |
| Free model "returns nothing" | It's a rate limit, not a harness bug — use a paid model |
grep -c in the verdict aborts the script under set -e on a zero (clean baseline) match |
Guard the grep (` |
| Omitting the prompt-parity control | A skeptic will assume the gain is just "you told it to review" |
| "Same prompt, only difference is the plugin" | The treatment prompt invokes the workflow — disclose it, don't claim parity |
| Publishing n=1 as a benchmark | Call them recorded sessions; state every n |
Reference
- Harness + prompts + pre-registrations + raw transcripts:
tests/manual/with-without-eval/ - Public artifact produced from it:
docs/src/content/docs/guides/with-without-systematic.mdx - Isolation lineage:
docs/solutions/best-practices/reliable-cli-integration-testing-2026-04-26.md