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 skills add Owl-Listener/designpowers --skill heuristic-evaluationgit clone --depth 1 https://github.com/Owl-Listener/designpowersWrote 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/owl-listener/designpowers/heuristic-evaluation)<a href="https://agentmods.dev/skills/owl-listener/designpowers/heuristic-evaluation"><img src="https://agentmods.dev/badge/skills/owl-listener/designpowers/heuristic-evaluation.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 5.1 | $0.00079 | $0.01139 |
| Opus 5 | $0.00039 | $0.00570 |
| Sonnet 5 | $0.00016 | $0.00228 |
| Haiku 4.5 | $0.00008 | $0.00114 |
Grade A, and why
heuristic-evaluation 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 7d 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 — 86 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Heuristic Evaluation
Heuristic evaluation is the usability lens on a build. Where designpowers-critique asks "does this match the plan?" and the accessibility review asks "can everyone access this?", heuristic evaluation asks "will people actually be able to use this without getting lost, confused, or stuck?" This skill dispatches the heuristic-evaluator agent and integrates its findings with the other reviewers.
When to Use
- After
design-buildercompletes a build — run alongsidedesignpowers-critiqueand the accessibility review, not after them - Before a fix round, so usability findings are reconciled with craft and accessibility findings together
- When a flow feels confusing but you can't articulate why — the heuristics name the problem
- When evaluating an existing design (see
using-designpowers→ Review Mode), not just freshly built work
This skill is not optional after a build. Skipping it is a Red Flag (see using-designpowers). Usability problems that craft critique and accessibility audits both miss are exactly what this catches.
Process
Step 1: Confirm Inputs Exist
Before dispatching, assemble:
- The build to evaluate (running app, prototype, or screenshots — test what was built, not the spec)
- The design brief (from
design-discovery) — for the key tasks to walk through - The personas (from
inclusive-personas) — each persona's primary task gets a cognitive walkthrough design-state.md— the shared state the agent will read and update
If there is no brief or no list of key tasks, the cognitive walkthrough has nothing to walk through. Go back and capture the key tasks first.
Step 2: Dispatch the heuristic-evaluator Agent
Dispatch the heuristic-evaluator agent (see agents/heuristic-evaluator.md). It will:
- Evaluate the interface against Nielsen's 10 heuristics, citing specific violations with evidence (H1–H10)
- Run a cognitive walkthrough of every key task — four questions per step
- Analyse error paths, not just happy paths — recovery, undo, back navigation, dead ends
- Assess learnability (first-time user) and efficiency (repeat user)
- Acknowledge what works well, not only what fails
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.
- 7d ago First seen · 86 lines · 79 tokens per session scan A e70c539257a6
heuristic-evaluation is a skill published in the GitHub repository Owl-Listener/designpowers (241 stars, last pushed 2mo ago), licensed MIT. It adds 79 tokens to every session and 1,139 once invoked, about $0.0004 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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