diff --git a/DEVELOPMENT.md b/DEVELOPMENT.md
new file mode 100644
index 0000000..88834b5
--- /dev/null
+++ b/DEVELOPMENT.md
@@ -0,0 +1,22 @@
+# Developing Sketch
+
+## Running tests
+
+* `go test ./...`
+* `cd loop/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_.*
+```
diff --git a/README.md b/README.md
index bde6893..9085f2b 100644
--- a/README.md
+++ b/README.md
@@ -29,6 +29,10 @@
 
 Join if you want! https://discord.gg/2xG3KEG3
 
+## Development
+
+See [DEVELOPMENT.md](DEVELOPMENT.md)
+
 ## Open Source
 
 Sketch is open source.
@@ -36,5 +40,5 @@
 Have a look around and mod away.
 
 If you want to run sketch entirely without the sketch.dev service, you can
-set the flag -skaband-addr="" and then provide an ANTHROPIC_API_KEY
+set the flag -skaband-addr="" and then provide an `ANTHROPIC_API_KEY`
 environment variable. (More LLM services coming soon!)