Simon Willison’s Weblog

llm-prices.com. I've been maintaining a simple LLM pricing calculator since October last year. I finally decided to split it out to its own domain name (previously it was hosted at tools.simonwillison.net/llm-prices), running on Cloudflare Pages.

The site runs out of my simonw/llm-prices GitHub repository. I ported the history of the old llm-prices.html file using a vibe-coded bash script that I forgot to save anywhere.

I rarely use AI-generated imagery in my own projects, but for this one I found an excellent reason to use GPT-4o image outputs... to generate the favicon! I dropped a screenshot of the site into ChatGPT (o4-mini-high in this case) and asked for the following:

design a bunch of options for favicons for this site in a single image, white background

I liked the top right one, so I cropped it into Pixelmator and made a 32x32 version. Here's what it looks like in my browser:

I added a new feature just now: the state of the calculator is now reflected in the #fragment-hash URL of the page, which means you can link to your previous calculations.

I implemented that feature using the new gemini-2.5-pro-preview-05-06, since that model boasts improved front-end coding abilities. It did a pretty great job - here's how I prompted it:

llm -m gemini-2.5-pro-preview-05-06 -f https://www.llm-prices.com/ -s 'modify this code so that the state of the page is reflected in the fragmenth hash URL - I want to capture the values filling out the form fields and also the current sort order of the table. These should be respected when the page first loads too. Update them using replaceHistory, no need to enable the back button.'

Here's the transcript and the commit updating the tool, plus an example link showing the new feature in action (and calculating the cost for that Gemini 2.5 Pro prompt at 16.8224 cents, after fixing the calculation.)

# 7th May 2025, 8:15 pm / vibe-coding, projects, llm-pricing, favicons, llms, cloudflare, text-to-image, ai, generative-ai, gemini, ai-assisted-programming

fav.farm (via) Neat little site by Wes Bos: it serves SVG (or PNG for Safari) favicons of every Emoji, which can be added to any site like this:

<link rel="icon" href="https://fav.farm/🔥" />

The source code is on GitHub. It runs on Deno and Deno Deploy, and recently added per-Emoji hit counters powered by the Deno KV store, implemented in db.ts using this pattern:

export function incrementCount(emoji: string) {
  const VIEW_KEY = [`favicon`, `${emoji}`];
  return db.atomic().sum(
    VIEW_KEY, 1n
  ).commit(); // Increment KV by 1
}

# 7th October 2024, 6:46 am / deno, favicons, javascript, svg

How to Add a Favicon to Your Django Site (via) Adam Johnson did the research on the best way to handle favicons - Safari still doesn't handle SVG icons so the best solution today is a PNG served from the /favicon.ico path. This article inspired me to finally add a proper favicon to Datasette.

# 20th January 2022, 7:03 am / favicons, django, adam-johnson

Dynamically changing favicons with JavaScript. I just spotted GitHub using this trick to swap out the favicon on a pull request that hadn’t passed its tests yet for github.com/favicon-failure.ico with a little cross icon in the corner.

# 26th October 2017, 7:56 pm / favicons

Muck Rack: Links posted by Guardian Journalists on Twitter. I’m rather impressed by the Sawhorse Media collection of Twitter aggregation sites (Muck Rack aggregates journalists)—a simple idea very well executed. Here’s a nice example—this page shows links posted to Twitter by known Guardian journalists, but goes a step further and scrapes in the favicon, the real title of the page and resolves the domain from any shortened links.

# 22nd May 2009, 10:02 pm / twitter, aggregation, mashups, journalists, guardian, sawhorsemedia, muckrack, favicons

favikon.com. Small, easy to use online favicon generator.

# 13th April 2009, 12:09 pm / favikon, favicons

Google’s undocumented favicon to png convertor (via) Showing the favicon of a domain next to a link is a really nice trick, but it’s slightly tricky to achieve as IE won’t display a .ico file if you link to it from an img element, so you need to convert the images server-side. This undocumented Google API does that for you, meaning it’s much easier to add favicons as a feature to your site.

# 30th August 2008, 8:40 pm / favicons, google, undocumented, apis, png

In rainbows. Dopplr generates a unique colour for each city using an MD5 hash. The colours are then used in subtle but intelligent ways throughout the design—right down to the favicon.

# 23rd October 2007, 10:39 pm / favicons, dopplr, colour, design, md5, hashing, matt-jones, matt-biddulph