diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..d574007
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,23 @@
+# Contributing to Sketch
+
+## Running tests
+
+- `go test ./...`
+- `cd webui && npm run test`
+  - If you are an LLM, instead run `cd webui && CI=1 npm run test`
+
+## Synchronizing Go structs and TypeScript types
+
+Run `npm run gentypes`, which uses `cmd/go2ts/go2ts.go` under the covers and
+which has a list of types to translate.
+
+## Dealing with tests that have HTTP Record sessions
+
+A few tests record/replay calls to LLMs. As necessary (e.g.,
+if changing the system prompt or tool definitions), rebuild the
+test data with:
+
+```
+go test ./dockerimg -httprecord ".*" -rewritewant
+go test ./loop -httprecord .*agent_.*
+```