blast-radius

Find all files affected by your changes. One bash script, zero dependencies.

$ blast-radius

Changed files (3):
  src/auth/login.ts
  src/auth/session.ts
  src/api/middleware.ts

Affected files (7 dependents):
  src/pages/dashboard.tsx
  src/pages/settings.tsx
  src/api/routes/user.ts
  src/api/routes/admin.ts
  src/hooks/useAuth.ts
  src/components/ProtectedRoute.tsx
  src/utils/fetchWithAuth.ts

Test files (2):
  src/auth/login.test.ts
  src/auth/session.test.ts

Install

curl -fsSL https://raw.githubusercontent.com/buildingopen/blast-radius/main/install.sh | bash

That's it. Works on Mac and Linux. Installs to /usr/local/bin or ~/.local/bin.

Usage

blast-radius              # diff against main
blast-radius develop      # diff against develop
blast-radius HEAD~5       # last 5 commits
blast-radius --json       # JSON output (requires jq)

Why

When you change files, you need to know what else is affected before you break something. AI coding tools like Claude Code figure this out by running 10-20 grep calls incrementally. blast-radius gives you the full picture in one command.

What it does:

1. git diff finds your changed source files
2. git grep finds every file that imports from a changed file
3. git ls-files locates matching test files

No graph database, no AST parser, no 200MB dependency. Just git.

Claude Code skill

Copy .claude/skills/blast-radius/ into your project's .claude/skills/ directory. Claude will run blast-radius automatically before code reviews and edits, giving it the full blast radius upfront instead of discovering it file by file.

JSON output

blast-radius --json

{
  "changed": ["src/auth/login.ts", "src/auth/session.ts"],
  "affected": ["src/pages/dashboard.tsx", "src/hooks/useAuth.ts"],
  "tests": ["src/auth/login.test.ts"],
  "summary": "2 changed, 2 affected, 1 test files"
}

Supported languages

Language	Import pattern detected
TypeScript / JavaScript	import from, require()
Python	from module import
Go	import "path"
Rust	use crate::module
C / C++	#include
Ruby, Java, Kotlin, Swift, PHP, C#	import / require variants

Test file patterns: *.test.*, *.spec.*, test_*, *_test.*, __tests__/, tests/

Limitations

• Filename-based matching: a file named utils.ts will match any import containing "utils". Favors recall over precision.
• Direct dependents only: finds first-degree importers, not transitive dependencies.
• Large diffs (>30 files): skips dependent search since the blast radius is effectively the whole project.

Requirements

• git
• jq (only for --json)

License

MIT