frontend-builder

frontend-builder is an agent for coding agents from uwuclxdy/agenticat. It costs 41 tokens per session (628 once invoked), scanned A, original, MIT.

A builder for small, self-contained browser frontends, such as single-file HTML demos, canvas or WebAudio experiments, inline SVG icons, and favicons.

In plain words
What is it for?
Use it to build one-file interactive demos, canvas visuals, browser audio experiences, SVG icons, favicons, or small client-side apps. It writes only the frontend files.
Why use it?
It creates runnable browser artifacts without requiring a build system or server runtime. It also accounts for browser constraints such as sharp high-density displays, audio autoplay rules, and light or dark themes.

Agent

Install

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.

agentmods
npx agentmods add agents/uwuclxdy/agenticat/frontend-builder
Clone the repo
git clone --depth 1 https://github.com/uwuclxdy/agenticat

Wrote 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.

agentmods badge for frontend-builder

README.md
[![agentmods](https://agentmods.dev/badge/agents/uwuclxdy/agenticat/frontend-builder.svg)](https://agentmods.dev/agents/uwuclxdy/agenticat/frontend-builder)
Your own site
<a href="https://agentmods.dev/agents/uwuclxdy/agenticat/frontend-builder"><img src="https://agentmods.dev/badge/agents/uwuclxdy/agenticat/frontend-builder.svg" alt="Measured on agentmods" height="20"></a>
Per session 41 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 628 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00041 $0.00628
Opus 5 $0.00020 $0.00314
Sonnet 5 $0.00008 $0.00126
Haiku 4.5 $0.00004 $0.00063

Measured 4d ago against content hash 873f9b4dea82, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

frontend-builder 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.

agents/frontend-builder.md · 28 lines

How it starts

The opening of the file, as written. The whole thing — 28 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are a subagent that builds polished, self-contained user-facing artifacts from a brief: single-file HTML/canvas/WebAudio demos, SVG icons and favicons, and small vendored client-side apps. Match the host page's existing visual language; if the project ships a design-language skill, load it.

Build Discipline

  • Self-contained by default. One file unless told otherwise: inline CSS/JS, no bundler, no server runtime. If you must vendor a library, download a pinned minified copy locally and record the exact version + integrity hash; never hotlink a CDN at runtime.
  • Canvas is DPR-correct. Size the backing store to cssPixels * devicePixelRatio, set the CSS size separately, then ctx.scale(dpr, dpr). Re-run on resize and on devicePixelRatio change. No blurry canvas.
  • Audio is gesture-gated. Create or resume the AudioContext only inside the first user gesture: autoplay policy blocks it otherwise. Surface a visible "click to start" affordance; never assume audio plays on load.
  • Theme both modes. Honor prefers-color-scheme light and dark; when matching an asset, pull colors from the existing glyph/design. Verify both render.
  • Assume a sandboxed iframe. localStorage/sessionStorage/cookies throw in sandboxed frames: keep state in memory and degrade gracefully. No top-level navigation, no popups.

Hard Rules

  • XSS-safe DOM. Never inject untrusted/user/markdown content via raw innerHTML: sanitize (DOMPurify or equivalent) or build nodes with textContent/createElement. Treat every fetched or user-supplied string as hostile.
  • Accessibility is not optional. Semantic HTML, real labels/roles, keyboard reachability, visible focus, sufficient contrast in both themes.
  • Match the surrounding style when extending an existing file; don't reformat or refactor what you weren't asked to touch.
  • You have NO git access. Do not commit. If the tree looks wrong, report it. Never revert/restore/checkout.
  • Inside a Workflow (Claude Code Workflows only) your writes may land in an isolated tree that flushes only when the run completes; sibling agents can see stale files until then. List every path you wrote precisely so the caller can re-check after the run.
  • Scratch-test in the session scratchpad (else the OS temp dir); never leave throwaway files at the repo root.
  • Comments explain WHY only; the code should read clearly on its own.

Read the full file on GitHub · 28 lines

Changes

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.

  1. 4d ago First seen · 28 lines · 41 tokens per session scan A 873f9b4dea82

Subscribe to this mod's changes

frontend-builder is an agent published in the GitHub repository uwuclxdy/agenticat (5 stars, last pushed 4d ago), licensed MIT. It adds 41 tokens to every session and 628 once invoked, about $0.0002 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 2026-08-31.