Simon Willison’s Weblog

Inside .git. This single diagram filled in all sorts of gaps in my mental model of how git actually works under the hood. # 25th January 2024, 2:59 pm

Notes on using a single-person Mastodon server. Julia Evans experiences running a single-person Mastodon server (on masto.host—the same host I use for my own) pretty much exactly match what I’ve learned so far as well. The biggest disadvantage is the missing replies issue, where your server only shows replies to posts that come from people who you follow—so it’s easy to reply to something in a way that duplicates other replies that are invisible to you. # 16th September 2023, 10:35 pm

Lima VM—Linux Virtual Machines On macOS (via) This looks really useful: “brew install lima” to install, then “limactl start default” to start an Ubuntu VM running and “lima” to get a shell. Julia Evans wrote about the tool this morning, and here Adam Gordon Bell includes details on adding a writable directory (by default lima mounts your macOS home directory in read-only mode). # 10th July 2023, 7:01 pm

Implement DNS in a weekend (via) Fantastically clear and useful guide to implementing DNS lookups, from scratch, using Python’s struct, socket and dataclass modules—Julia Evans plans to follow this up with one for TLS which I am very much looking forward to. # 12th May 2023, 6:14 pm

Writing Javascript without a build system (via) Julia Evans perfectly captures why I prefer not to use build systems in the majority of my projects that use JavaScript: “... my experience with build systems (not just Javascript build systems!), is that if you have a 5-year-old site, often it’s a huge pain to get the site built again. And because most of my websites are pretty small, the advantage of using a build system is pretty small.” # 18th February 2023, 5:25 am

Examples of floating point problems (via) I learned so much practical stuff from this post by Julia Evans. There are no 32-bit floating point numbers between 262144.0 and 262144.03125, which breaks code that attempts to keep incrementing by 0.01. I knew about the JavaScript tweet ID problem (JavaScript can’t handle numbers like 1612850010110005250) but I didn’t realize it affected jq as well. Lots more great examples in here. # 13th January 2023, 3:41 pm

sqlite-utils: a nice way to import data into SQLite for analysis (via) Julia Evans on my sqlite-utils Python library and CLI tool. # 13th May 2022, 6:17 pm

New tool: an nginx playground. Julia Evans built a sandbox tool for interactively trying out an nginx configuration and executing test requests through it. I love this kind of tool, and Julia’s explanation of how they built it using a tiny fly.io instance and a network namespace to reduce the amount of damage any malicious usage could cause is really interesting. # 24th September 2021, 6:44 pm

How to look at the stack with gdb. Useful short tutorial on gdb from first principles. # 24th May 2021, 6:23 pm

No feigning surprise (via) Don’t feign surprise if someone doesn’t know something that you think they should know. Even better: even if you are surprised, don’t let them know! “When people feign surprise, it’s usually to make them feel better about themselves and others feel worse.” # 17th May 2021, 4:30 pm

entr: rerun your build when files change. “WHY DID NOBODY TELL ME ABOUT THIS BEFORE?!?!” is one of my favourite genres of blog post. # 1st July 2020, 3:58 pm

SQL queries don’t start with SELECT. This is really useful. Understanding that SELECT (and associated window functions) happen after the WHERE, GROUP BY and HAVING helps explain why you can’t filter a query based on the results of a window function for example. # 3rd October 2019, 8:56 pm

Build impossible programs. Delightful talk by Julia Evans describing how she went about building a Ruby profiler in Rust despite having no knowledge of Ruby internals and only beginner’s knowledge of Rust. # 19th September 2018, 6:38 pm

Using flamegraphs. I really like flamegraphs as a profiling tool—we have support for them baked into our Tikibar debugging toolbar at Eventbrite—but interpreting them isn’t particularly intuitive on first glance. Julia Evans has put together a great explanation of how to read them as part of the documentation for her rbspy Ruby profiler. # 21st March 2018, 8:56 pm

How do Ruby & Python profilers work? Julia Evans: “As a precursor to writing a Ruby profiler I wanted to do a survey of how existing Ruby & Python profilers work.” # 18th December 2017, 12:12 pm

How to teach technical concepts with cartoons. Julia Evans: “This post is about a few patterns I use when illustrating ideas about computers. If you are interested in using drawings to teach people about your very favorite computer topics, hopefully this will help you!” # 28th October 2017, 2:55 pm