Simon Willison’s Weblog

Anthropic API: Text editor tool (via) Anthropic released a new "tool" today for text editing. It looks similar to the tool they offered as part of their computer use beta API, and the trick they've been using for a while in both Claude Artifacts and the new Claude Code to more efficiently edit files there.

The new tool requires you to implement several commands:

• view - to view a specified file - either the whole thing or a specified range
• str_replace - execute an exact string match replacement on a file
• create - create a new file with the specified contents
• insert - insert new text after a specified line number
• undo_edit - undo the last edit made to a specific file

Providing implementations of these commands is left as an exercise for the developer.

Once implemented, you can have conversations with Claude where it knows that it can request the content of existing files, make modifications to them and create new ones.

There's quite a lot of assembly required to start using this. I tried vibe coding an implementation by dumping a copy of the documentation into Claude itself but I didn't get as far as a working program - it looks like I'd need to spend a bunch more time on that to get something to work, so my effort is currently abandoned.

This was introduced as in a post on Token-saving updates on the Anthropic API, which also included a simplification of their token caching API and a new Token-efficient tool use (beta) where sending a token-efficient-tools-2025-02-19 beta header to Claude 3.7 Sonnet can save 14-70% of the tokens needed to define tools and schemas.