Simon Willison’s Weblog

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5 posts tagged “gif”

2026

Agentic Engineering Patterns >

GIF optimization tool using WebAssembly and Gifsicle

I like to include animated GIF demos in my online writing, often recorded using LICEcap. There's an example in the Interactive explanations chapter.

These GIFs can be pretty big. I've tried a few tools for optimizing GIF file size and my favorite is Gifsicle by Eddie Kohler. It compresses GIFs by identifying regions of frames that have not changed and storing only the differences, and can optionally reduce the GIF color palette or apply visible lossy compression for greater size reductions.

Gifsicle is written in C and the default interface is a command line tool. I wanted a web interface so I could access it in my browser and visually preview and compare the different settings. [... 1,603 words]

# 2nd March 2026, 4:35 pm / claude, ai, claude-code, llms, prompt-engineering, webassembly, coding-agents, tools, generative-ai, gif, agentic-engineering

2020

gifcap (via) This is really neat: a purely client-side implementation of animated gif screen capture, using navigator.mediaDevices.getDisplayMedia for the screen capturing, mithril for the UI and the gif.js pure JavaScript GIF encoding library to render the output.

# 30th March 2020, 9:29 pm / gif, javascript, screencast

2013

Should I ever use GIF image format for non animated elements?

These days probably not—anything non-animated that you would use a GIF for is generally better as a PNG.

[... 37 words]

2009

2008

Poking new holes with Flash Crossdomain Policy File. This is an old article from 2006 which describes the crossdomain.xml hidden in a GIF exploit I referred to in an earlier post (scroll down to the appendix for an example). As far as I know the Flash Player’s crossdomain.xml parser has been tightened up since.

# 1st July 2008, 4:12 pm / crossdomainxml, flash, gif, security