Anthropic launches mods to customize Claude Code

Anthropic has launched Mods, a new TypeScript-based extensibility layer for its Claude Code command-line interface and desktop application. Available at no additional cost, these mods allow developers to intercept events, rewrite prompts, render custom user interface components, and register new commands. Unlike previous settings hooks that only observed events, mods function as middleware with the ability to observe, rewrite, or short-circuit actions like tool calls and user prompts.

To demonstrate the capabilities of the new system, Anthropic provided three reference implementations. Token Weather uses roughly 80 lines of code to display context usage and a 12-turn sparkline above the prompt. Blast Radius acts as a command guard, intercepting destructive Bash commands like 'rm -rf' or 'git reset --hard' to prompt users with confirmation controls. Replay Theater records edits during a turn and uses a new '/replay' command to step through diffs. Built-in Claude Code features, including the '/diff' command and 'AGENTS.md' support, have also been converted into mods, meaning developers can now disable or replace them entirely.

Because mods run with full machine access and are unsandboxed, Anthropic advises users to only install them from trusted publishers. To mitigate security risks, Team and Enterprise plans automatically load a security-focused mod called 'sec-default' first, preventing subsequent user mods from overriding established permission rules. For developers building their own extensions, Claude Code can generate a mod from a natural-language prompt and hot-reload it directly into an active session. Developers can also use the 'claude plugin validate' command to inspect event handlers and 'claude plugin test' to run test files against the runtime.