What is filetree-skill?

filetree is a plugin for Claude Code (Anthropic's AI coding assistant) that solves a specific and repeatable problem: every time you start a new Claude Code session on a codebase, the AI has to rediscover the project layout from scratch by scanning directories and reading files. That discovery work costs tokens and takes time, and it cannot be reused between sessions. The plugin's answer is a file called FILETREE.md, checked into the repository alongside the code. It contains one line per file in the project, with a plain-English description of what that file does and a short hash of the file's contents. When Claude Code reads FILETREE.md at the start of a session, it gets an instant overview of the whole project in a few hundred tokens, rather than spending dozens of tool calls on ls, grep, and file reads. Three commands drive the workflow. The init command generates FILETREE.md from scratch by scanning the repo and asking the AI to write a one-line summary for each file. The update command syncs the manifest after code changes: it uses git to detect added, removed, renamed, and changed files, then asks the AI only about the ones that actually changed. Files that were modified but whose purpose stayed the same get marked UNCHANGED, which means only the hash is refreshed, not the description. The lint command checks whether the manifest is out of date without making any changes, and exits with an error code if it finds drift, making it usable in CI. The plugin requires Python 3.9 or newer and has no third-party dependencies beyond git. It is installed through Claude Code's plugin marketplace with a single command. The README notes it will not run background processes, build a search index, or auto-commit anything. It is released under the MIT license.