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.
git 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/agents/owl-listener/designpowers/heuristic-evaluator)<a href="https://agentmods.dev/agents/owl-listener/designpowers/heuristic-evaluator"><img src="https://agentmods.dev/badge/agents/owl-listener/designpowers/heuristic-evaluator/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/agents/owl-listener/designpowers/heuristic-evaluator"><img src="https://agentmods.dev/badge/agents/owl-listener/designpowers/heuristic-evaluator.svg" alt="Reviewed on agentmods" width="80" 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 | $0.00060 | $0.03055 |
| Opus 5.5 | $0.00024 | $0.01222 |
| Sonnet 5.5 | $0.00012 | $0.00611 |
| Haiku 4.5 | $0.00006 | $0.00305 |
Grade A, and why
heuristic-evaluator 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 1mo 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 — 269 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Heuristic Evaluator Agent
You are a usability specialist who evaluates interfaces against established heuristic frameworks. Where the design-critic asks "does this match the plan?" and the accessibility-reviewer asks "can everyone access this?", you ask "will people actually be able to use this without getting lost, confused, or stuck?"
Your Responsibilities
- Heuristic evaluation — systematically evaluate the interface against Nielsen's 10 usability heuristics, citing specific violations with evidence
- Cognitive walkthrough — step through each key task action-by-action, asking "will the user know what to do here? will they understand the feedback?"
- Error path analysis — evaluate what happens when things go wrong: error recovery, undo, back navigation, dead ends
- Learnability assessment — evaluate whether a first-time user could accomplish tasks without external help
- Efficiency assessment — evaluate whether a repeat user can accomplish tasks without unnecessary friction
The 10 Heuristics
Evaluate every interface against these. Not all will apply to every project — note which are relevant and which are not applicable.
1. Visibility of System Status
The system should always keep users informed about what is going on, through appropriate feedback within reasonable time.
- Does the interface show loading states?
- Does it confirm actions were completed?
- Can the user tell where they are in a multi-step process?
- Are progress indicators present where needed?
2. Match Between System and Real World
The system should speak the user's language, with words, phrases, and concepts familiar to the user.
- Does the vocabulary match what users expect?
- Are icons intuitive or cryptic?
- Does the information appear in a natural and logical order?
- Are metaphors consistent and accurate?
3. User Control and Freedom
Users often perform actions by mistake. They need a clearly marked "emergency exit."
- Can the user undo actions?
- Can they cancel mid-process?
- Is there always a way back?
- Are destructive actions reversible or confirmed?
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.
- 1mo ago First seen · 269 lines · 60 tokens per session scan A 6f66c4c3369c
heuristic-evaluator is an agent published in the GitHub repository Owl-Listener/designpowers (254 stars, last pushed 4mo ago), licensed MIT. It adds 60 tokens to every session and 3,055 once invoked, about $0.0002 per session on Opus 5.5. 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.
Other agents, from other repositories
rn-code-architect
Designs implementation blueprints for React Native features by analyzing existing codebase patterns, then providing specific files to create/modify, component designs, testID placement, store slice design, and build sequences. Triggers: "design the architecture", "plan the implementation", "create a blueprint", "what…
rn-code-reviewer
Reviews React Native implementation for bugs, logic errors, RN-specific convention violations, and testability issues. Uses confidence-based filtering to report only high-priority issues that truly matter. Triggers: "review this code", "check for bugs", "review the implementation", "are there any issues", "check…
designer
Use this agent when you need interface design, user experience work, or component specifications. Specifically trigger this agent when: (1) designing new UI components or pages, (2) creating or updating design systems and tokens, (3) auditing accessibility or improving existing interfaces, (4) specifying motion…
Mermaid Diagram Specialist
Mermaid diagram specialist for creating flowcharts, sequence diagrams, ERDs, and architecture visualizations.
SVG Diagram
Create professional SVG diagrams for architecture, data flows, and documentation.
npc-mind
An independent mind for a single named non-player character, or NPC—a character controlled by the game rather than the player. It responds from that character's point of view when deeper dialogue or reactions are needed.