Simon Willison’s Weblog

Claude Projects. New Claude feature, quietly launched this morning for Claude Pro users. Looks like their version of OpenAI's GPTs, designed to take advantage of Claude's 200,000 token context limit:

You can upload relevant documents, text, code, or other files to a project’s knowledge base, which Claude will use to better understand the context and background for your individual chats within that project. Each project includes a 200K context window, the equivalent of a 500-page book, so users can add all of the insights needed to enhance Claude’s effectiveness.

You can also set custom instructions, which presumably get added to the system prompt.

I tried dropping in all of Datasette's existing documentation - 693KB of .rst files (which I had to rename to .rst.txt for it to let me upload them) - and it worked and showed "63% of knowledge size used".

This is a slightly different approach from OpenAI, where the GPT knowledge feature supports attaching up to 20 files each with up to 2 million tokens, which get ingested into a vector database (likely Qdrant) and used for RAG.

It looks like Claude instead handle a smaller amount of extra knowledge but paste the whole thing into the context window, which avoids some of the weirdness around semantic search chunking but greatly limits the size of the data.

My big frustration with the knowledge feature in GPTs remains the lack of documentation on what it's actually doing under the hood. Without that it's difficult to make informed decisions about how to use it - with Claude Projects I can at least develop a robust understanding of what the tool is doing for me and how best to put it to work.

No equivalent (yet) for the GPT actions feature where you can grant GPTs the ability to make API calls out to external systems.

# 4:03 pm / ai, openai, prompt-engineering, chatgpt, llms, anthropic, claude, rag

Polyfill supply chain attack hits 100K+ sites (via) Short version: if you are loading assets from the polyfill.io domain you need to remove that right now: the new owners of the domain (as of a few months ago) appear to be using it to serve malicious JavaScript.

polyfill.io was a fascinating service. It was originally developed and supported by the Financial Times, but span off as a separate project several years ago.

The key idea was to serve up a set of JavaScript polyfills - pieces of code that implemented missing web platform features for older browsers - dynamically, based on the incoming user-agent. This required a CDN that varied its output dynamically based on the user-agent, hence the popularity of the single hosted service.

Andrew Betts, the original author of the service, has been warning people to move off it since February 2024:

If your website uses polyfill.io, remove it IMMEDIATELY.

I created the polyfill service project but I have never owned the domain name and I have had no influence over its sale.

He now works for Fastly, which started offering a free polyfill-fastly.io alternative in February. Andrew says you probably don't need that either, given that modern browsers have much better compatibility than when the service was first introduced over a decade ago.

There's some interesting additional context in a now-deleted GitHub issue, preserved here by the Internet Archive.

Usually one answer to protecting against this style of CDN supply chain attack would be to use SRI hashes to ensure only the expected script can be served from the site. That doesn't work here because the whole point of the service is to serve different scripts to different browsers.

# 10:17 pm / javascript, security, supply-chain