diff --git a/.env.example b/.env.example
new file mode 100644
index 0000000..4dde3de
--- /dev/null
+++ b/.env.example
@@ -0,0 +1,4 @@
+# Save as .env, fill in keys, gets automatically sourced by `nix develop`
+export INFURA_API_KEY="..."
+export ETHERSCAN_API_KEY="..."
+export PROVIDER="ethers"  # or "viem"
diff --git a/README.md b/README.md
index 7a214e3..e20b6fe 100644
--- a/README.md
+++ b/README.md
@@ -172,7 +172,7 @@ console.log("Resolved to:", address);
 ## Development
 
 ```console
-$ cat .env
+$ cat .env  # Write an .env file with your keys, or `cp .env.example .env`
 export INFURA_API_KEY="..."
 export ETHERSCAN_API_KEY="..."
 $ nix develop  # Or use your system's package manager to install node/ts/etc