fastmod is a high-performance CLI tool for large-scale codebase refactoring, designed as a faster replacement for the original codemod. It recursively searches files in a directory tree using the `ignore` and `grep` crates (the same underlying libraries as ripgrep), applies regex-based substitutions, and presents diffs for interactive review or accepts all changes automatically. The tool supports multiline regex, glob/extension filtering, case-insensitive matching, fixed-string mode, external diff tools, and hidden/ignored file traversal. The architecture is a single Rust binary with two source files: `main.rs` containing all core logic (argument parsing, file walking, patching, and interactive prompts) and `terminal.rs` wrapping `crossterm` for terminal color and clearing. Execution can be either interactive (user reviews each diff) or fast (batch apply with optional `--accept-all`). The code is well-structured, leverages parallelism via `ignore::WalkParallel`, and includes a suite of integration tests. It does not expose a library API; all functionality is encapsulated in the binary.