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Claude Code builds and browser-tests a GIF optimizer

Willison asked Claude Code for web to compile Gifsicle to WebAssembly and build a preview interface. The agent used Rodney to exercise the page and fix UI bugs during implementation.

Added simonwillison.netAgent: Claudevia Claude Code
TRY A BOUNDED VERSION

Prompt to try

Editorial adaptation, not the source author’s exact prompt. Replace bracketed inputs and review tool permissions first.

Build a local browser wrapper for [CLI tool]. Reuse the repository conventions, retain upstream attribution and include a reproducible build script. Test upload, settings, preview and download using browser automation. Report observed results and remaining limitations; stop before publishing.

What happened

Willison shows the working optimizer and reports browser testing that caught minor UI bugs.

Reported by Simon Willison

How the agent did it

  1. Inspect existing tools and compile Gifsicle for a browser runtime.
  2. Build upload, compression previews and downloadable results.
  3. Exercise the interface with Rodney and repair observed bugs; preserve the build patch and attribution.

Where a person stepped in

Willison watched progress and added requirements for reproducible build files and upstream credit.

A person approved each step before the agent continued.

More details

About this account

Claude selected build and UI details and used a browser tool to check and revise its own output.

Annotated firsthand prompt and session links. Source has no publication date; sourcePublished is omitted from this record.

Credit: Simon Willison

Source checked 14 Oct 2026

Tools and topics

Claude Code · Gifsicle · WebAssembly · Emscripten · Rodney

Code · Testing

Editorial completeness: 100/100. Measures documented fields, not agent performance or verified outcomes.

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