Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/understudylabs/understudy-agent-tools/compare-trajectoriesnpx skills add understudylabs/understudy-agent-tools --skill compare-trajectoriesgit clone --depth 1 https://github.com/understudylabs/understudy-agent-toolsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/understudylabs/understudy-agent-tools/compare-trajectories)<a href="https://agentmods.dev/skills/understudylabs/understudy-agent-tools/compare-trajectories"><img src="https://agentmods.dev/badge/skills/understudylabs/understudy-agent-tools/compare-trajectories.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00100 | $0.02514 |
| Opus 5 | $0.00050 | $0.01257 |
| Sonnet 5 | $0.00020 | $0.00503 |
| Haiku 4.5 | $0.00010 | $0.00251 |
Grade A, and why
compare-trajectories scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 173 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Compare Trajectories
Use this worker when
../compare-model-sweep/SKILL.md has already
told you that model A and model B score differently on a frozen eval, and the
next question — the one that decides whether to spend RL budget — is HOW their
trajectories differ, step by step, on the same tasks. A pass-rate delta is a
scalar; it cannot tell you whether the stronger model wins because it tries
longer, because it knew the right endpoint, or because the weaker model's
tool-calls were malformed. Those three answers point at three different fixes —
RL, retrieval/world-knowledge, or decoding/prompt — and only a per-task
trajectory diff separates them.
This skill aligns two (or more) run exports by task id, builds the outcome-delta
matrix, computes behavioral divergence on shared tasks, classifies each
reachable-gap task, and counts how many clean warm-start trajectories the
comparison yields. It reads trajectory JSON that already exists on disk; it does
not run models. To produce the trajectories, run
../run-local-model-lab/SKILL.md or
../compare-model-sweep/SKILL.md first.
Safety Gates
- Local-first, no upload. Trajectory exports contain full message bodies and
tool I/O. Keep the diff, the matrix, and the report under
.understudy/; do not paste trajectories or task content into external services. - Flag small N. A reachable-gap set of 3 tasks is an anecdote, not a capability claim. State the shared-task count and the per-class count on every verdict, and refuse to generalize below a stated floor (default N<10 → "directional only").
- Segregate frozen holdout. If either export includes holdout/frozen rows,
say so and split the matrix into train/dev vs holdout sections — never
warm-start from holdout trajectories, and never report a holdout-derived gap as
a training signal. Prefer a hash-stamped selection from
../curate-trajectories/SKILL.md. - No vibes. "B is better" must be backed by the per-task matrix and the divergence metrics, never by reading a few transcripts. The gap classification is a hypothesis to confirm, not proof — label it as such.
- Make all token/cost/step claims from the export fields, not memory.
What ships with it
3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 4d ago First seen · 173 lines · 100 tokens per session scan A f2ce21567658
compare-trajectories is a skill published in the GitHub repository understudylabs/understudy-agent-tools (16 stars, last pushed 4d ago), licensed MIT. It adds 100 tokens to every session and 2,514 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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