FastLint

FastLint checks all your files in any programming language, making vibe coding safer and faster.

Rather than reimplementing analyses, it bundles best-in-class open-source checkers from crates.io.

Install

From crates.io:

cargo install fastlint

From a local checkout:

cargo install --path .

Usage

fastlint                  # check the current directory
fastlint source/frontend  # check a specific directory or file
fastlint --json           # emit diagnostics as a JSON array

.gitignore, .ignore, hidden files, and obvious binary/lock files are skipped automatically.

Checks

Rule	Severity	Source
typos	warning	typos source-code spell-checker
merge-conflict	error	unresolved <<<<<<< / ======= / >>>>>>> markers
trailing-whitespace	warning	trailing spaces/tabs at end of line

Exit codes

Code	Meaning
0	no errors (warnings allowed)
1	one or more error diagnostics
2	usage error (e.g. path does not exist)