diff --git a/README.md b/README.md
new file mode 100644
index 0000000..f900a07
--- /dev/null
+++ b/README.md
@@ -0,0 +1,33 @@
+# Advent of Code 2023
+
+[Puzzle site](https://adventofcode.com/2023).
+
+# Speed
+
+Ahead-of-time compiled with `PublishAot`, M1 Max.
+The format is: "answer part1\ntime\nanswer part2\ntime\n...", with possible extra lines indicating how long it took to parse the input if I happen to have split that out.
+
+After day 3:
+
+```
+54304
+0.549458ms
+54418
+0.710375ms
+2727
+0.119959ms
+56580
+0.155708ms
+0.1395ms parse
+540131
+0.1395ms
+86879020
+0.840791ms
+4.144166ms total
+```
+
+# Building yourself
+
+Note that `PublishAot` assumes a lot of stuff about your environment, which is not necessarily true.
+The given flake should allow you to complete the publish except for a linking stage at the end: the publish will print out a failed command line, and you'll have to strip out some `-o` flags from it and run it manually.
+Then run `dotnet publish` again and it should succeed.