Function-call edits (structured replacements, not full rewrite)

README.md

@@ -7,9 +7,25 @@ The workflow:
 - Run the command, write instructions on what you want changed.
 - Enjoy the sassy comments.
 
-This tool calls the openai api. You'll need your own api key to use it.
-Use `refac login` to enter your api key. It will be saved in your home directory
-for future use. See [your api usage](https://platform.openai.com/account) .
+This tool calls the Anthropic (Claude) API by default — bring your own API key.
+Use `refac login` to enter it; the key is saved in your home directory for future
+use. See [your API usage](https://console.anthropic.com/settings/usage).
+
+OpenAI is still supported: set `provider = "openai"` in
+`~/.config/refac/config.toml` (or `REFAC_PROVIDER=openai`), then `refac login`.
+
+Config (`~/.config/refac/config.toml`, all optional):
+
+```toml
+provider = "anthropic"    # or "openai"
+model = "claude-opus-4-8" # default per provider; or set REFAC_MODEL
+edit_mode = "tool"        # "tool" (default, Anthropic): structured edits via a
+                          # function call, not a full rewrite. "rewrite" = old
+                          # behavior. OpenAI always rewrites. Or set REFAC_EDIT_MODE.
+max_tokens = 16000        # Anthropic only
+```
+
+Keys may also be supplied via `ANTHROPIC_API_KEY` / `OPENAI_API_KEY` env vars.
 
 ## SETUP