typecover

Analyze TypeScript codebases for type safety coverage.

Scans your .ts/.tsx files for unsafe patterns like any, type assertions, @ts-ignore, non-null assertions, and more. Gives you a coverage percentage and letter grade so you can track type safety over time.

Why?

TypeScript's compiler tells you about errors, but it doesn't tell you how safe your types actually are. A codebase can compile cleanly while being full of any, as casts, and @ts-ignore escapes. typecover measures the gap.

Install

npm install -g typecover
# or
npx typecover ./src

Usage

# Analyze current directory
typecover

# Analyze specific path
typecover src/

# Set CI threshold (fails if coverage below 90%)
typecover src/ --threshold 90

# Show individual findings
typecover src/ --findings

# JSON output for tooling
typecover src/ --json

# Only check specific patterns
typecover src/ --patterns any-keyword,ts-ignore

# Quiet mode (summary only)
typecover src/ --quiet

What It Detects

Pattern	Severity	Description
any-keyword	High	const x: any
any-array	High	const x: any[]
any-return	High	function foo(): any
as-cast	Medium	x as string
angle-bracket-cast	Medium	<string>x
ts-ignore	High	// @ts-ignore
ts-expect-error	Medium	// @ts-expect-error
ts-nocheck	Critical	// @ts-nocheck
non-null-assertion	Low	obj!.prop
force-unwraps	Low	arr!

Coverage Grades

Range	Grade
98-100%	A+
95-97%	A
90-94%	A-
85-89%	B+
80-84%	B
75-79%	B-
70-74%	C+
65-69%	C
60-64%	C-
50-59%	D
0-49%	F

Programmatic API

const { analyze, formatReport, checkCI } = require('typecover');

const result = analyze('./src');
console.log(formatReport(result, { verbose: true, showFindings: true }));

if (!checkCI(result, 85)) {
  process.exit(1);
}

CI Integration

Add to your CI pipeline:

- name: Type coverage check
  run: npx typecover src/ --threshold 90

Exit code is 1 if coverage falls below the threshold.

Zero Dependencies

No external dependencies. Pure Node.js.

License

MIT