Effective HTML is a collection of agent skills for creating self-contained HTML artifacts such as wireframes, interactive prototypes, plans, diagrams, reports, and tools. It helps coding agents turn reference material and prompts into visual, usable HTML deliverables, and the catalogue entries are its installable skills and plugins.
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 plannotator/effective-html --skill html-prototypegit clone --depth 1 https://github.com/plannotator/effective-htmlWrote 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/plannotator/effective-html/html-prototype)<a href="https://agentmods.dev/skills/plannotator/effective-html/html-prototype"><img src="https://agentmods.dev/badge/skills/plannotator/effective-html/html-prototype/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/skills/plannotator/effective-html/html-prototype"><img src="https://agentmods.dev/badge/skills/plannotator/effective-html/html-prototype.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Socket pass
- Snyk pass
- NVIDIA SkillSpector pass
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 | $0.00087 | $0.01167 |
| Opus 5.5 | $0.00035 | $0.00467 |
| Sonnet 5.5 | $0.00017 | $0.00233 |
| Haiku 4.5 | $0.00009 | $0.00117 |
Grade A, and why
html-prototype 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.
Copies of this mod
1 near-identical copy found in the catalogue:
- html-prototype — 94% identical, 8 lines differ
How it starts
The opening of the file, as written. The whole thing — 103 lines — stays where its author put it; the contents beside it link to each section on GitHub.
HTML Prototype
Build a credible model of a product decision. Match the artifact to the user's context instead of applying a recurring house style. The goal is not to make every possible screen. The goal is to make the important visual or behavioral question testable.
Choose the fidelity mode
Use one of two modes:
- Mockup: Create a polished, responsive, mostly static artifact when the open question is visual hierarchy, layout, typography, color, or product fit.
- Prototype: Create a working flow when the open question is navigation, input, state change, feedback, recovery, or transition.
Do not create a separate html-mockup skill. Do not add behavior merely to make a mockup seem more complete. If a user asks for both modes, preserve the same content and structure so changes in fidelity remain easy to compare.
Derive the direction from context
Inspect the conversation, supplied references, and project before designing. Look for design-system documentation, tokens, existing components, product screenshots, and nearby artifacts.
Authority runs in this order:
- The user's explicit visual and functional instructions.
- The project's established design language and interaction conventions.
- The product, audience, content, and scenario.
- Your own design judgment.
Before coding, settle:
- the user and critical job;
- the bounded scenario under review;
- mockup or prototype mode;
- the source of the visual direction;
- the relevant state model;
- the point where the real product would take over.
When no design system exists, create a specific direction from the subject and use case. Do not default to a gradient, a dark dashboard, interchangeable cards, or decorative metrics. A prototype for a field tool, an editorial workflow, and a financial approval should not feel like the same product.
When design-artifact is available and the visual
direction remains open, read and compose it with this skill. Use it to choose
the register, palette, type, and composition; keep this skill authoritative for
fidelity, state, and interaction completeness.
What ships with it
1 file 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.
- 1mo ago First seen · 103 lines · 87 tokens per session scan A 8987dda45224
html-prototype is a skill published in the GitHub repository plannotator/effective-html (3,717 stars, last pushed 6d ago), licensed MIT. It adds 87 tokens to every session and 1,167 once invoked, about $0.0003 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 skills, from other repositories
playground
Creates interactive HTML playgrounds — self-contained single-file explorers that let users configure something visually through controls, see a live preview, and copy out a prompt. Use when the user asks to make a playground, explorer, or interactive tool for a topic.
frontend-ui-engineering
Builds production-quality, accessible, responsive user-facing UIs. Use when building or modifying interfaces and pages, creating components, implementing layouts, meeting WCAG accessibility requirements, managing state, or when the output needs to look and feel production-quality rather than AI-generated.
frontend-design
Guidance for distinctive, intentional visual design when building new UI or reshaping an existing one. Helps with aesthetic direction, typography, and making choices that don't read as templated defaults.
web-design-engineer
Build or redesign polished browser-rendered visual artifacts with HTML/CSS/JavaScript/React: pages, dashboards, prototypes, slide decks, animations, UI mockups, and data visualizations. Use for visual front-end creation, design-system exploration, design critique, or explicit browser acceptance / QA of a web artifact.…
baseline-ui
Quickly deslop UI code by fixing spacing, hierarchy, typography, and small layout issues. Use when the interface needs a fast cleanup or polish pass.
migrate
Apply DESIGN, canon, and modules to every page in the inventory, producing a deployable static HTML site. Use to migrate or render the whole captured site into the redesigned static tree ("migrate the pages", "render the migrated site", "apply the design to all pages", "build the deployable site", "convert the…