Paste TypeScript code to instantly get cyclomatic complexity metrics, type coverage score, maintainability grade, and code quality analysis — no install required. Best free TypeScript code analyzer online.
This free TypeScript analyzer measures code quality without installing dependencies. Get instant metrics on complexity, type safety, maintainability, and potential issues. Perfect for code reviews, learning TypeScript best practices, and measuring code quality improvements.
Best TypeScript Static Analysis Tools – Features & Comparison
TypeScript static analysis tools examine your code without running it to find bugs, measure complexity, enforce style rules, and assess code quality. Here is how the main TypeScript code analysis tools compare:
Cyclomatic complexity is a quantitative measure of the number of linearly independent paths through your TypeScript code. It counts decision points: each if, else, for, while, case, catch, &&, and || adds 1 to the score. Higher cyclomatic complexity indicates code that's harder to test, maintain, and debug.
Score 1-5: Simple, maintainable TypeScript code — easy to understand and test
Score 6-10: Moderate complexity — refactoring recommended for clarity
Score 11-20: High complexity — significant refactoring needed to improve maintainability
Score 20+: Critical complexity — must refactor immediately to reduce technical debt
TypeScript functions with high cyclomatic complexity are harder to test and understand. Break complex functions into smaller, focused units to reduce complexity.
TypeScript Type Coverage Score – Measuring Type Safety
Type coverage measures the ratio of your TypeScript code that has explicit or inferred type information versus using the any type. A high type coverage percentage means better type safety; each any is an escape hatch that bypasses TypeScript's type checking entirely.
90-100% type coverage: Excellent — minimal use of 'any', strong type safety
70-90% type coverage: Good — most code is typed, some gaps remain
50-70% type coverage: Moderate — significant type safety gaps, refactoring recommended
Tools like typescript-coverage-report and type-coverage measure this across your entire repository. To improve type coverage, replace any with specific types or use unknown with proper type guards.
TypeScript Maintainability Index – Overall Code Quality Score
The maintainability index is a composite score combining cyclomatic complexity, lines of code, and Halstead volume (a measure of code density). Higher scores mean more maintainable code. This free TypeScript analyzer calculates maintainability grades from A (excellent) to F (critical):
Grade A (80-100): Simple, well-typed, low complexity — easy to maintain and extend
Grade B (65-79): Minor issues, generally maintainable — acceptable for production
Grade C (50-64): Moderate complexity or type safety gaps — refactoring recommended
Grade D (35-49): High complexity or significant 'any' usage — technical debt present
Grade F (below 35): Difficult to maintain, high risk of bugs — prioritize refactoring
How to Calculate TypeScript Function Metrics
TypeScript function metrics include: average lines of code per function, total function count, maximum nesting depth, and return type coverage. Functions should typically be under 50 lines of code. Large functions indicate they're doing too much and should be split into smaller, focused functions.
As a rule of thumb: files should have a single responsibility, functions should do one thing, and classes should have a narrow interface. A TypeScript file with 20+ functions or high nesting depth is a signal to refactor into multiple modules.
Common TypeScript Code Quality Issues
Common Code Quality Problems in TypeScript Projects
Excessive Use of 'any' Type in TypeScript
The any type bypasses TypeScript's type checking entirely, defeating the purpose of using TypeScript. Each any is a type safety hole. Instead of any, use specific types or unknown with type guards to maintain type safety.
High Cyclomatic Complexity in TypeScript Functions
Functions with many if/else branches, nested loops, and conditional operations become hard to understand and test. When cyclomatic complexity exceeds 10, break the function into smaller, focused units with single responsibilities.
Large TypeScript Files and Functions
Files over 300 lines or functions over 50 lines indicate poor separation of concerns. Split large TypeScript files into modules, and extract complex logic into separate functions. The Single Responsibility Principle improves maintainability.
Missing Return Type Annotations in TypeScript
Implicit return types make refactoring dangerous — changing implementation details can silently change the API contract. Always add explicit return type annotations to TypeScript functions to catch breaking changes during type checking.
Unused Variables and Dead Code in TypeScript
Variables declared but never used, unused imports, and unreachable code indicate incomplete refactoring. Enable noUnusedLocals and noUnusedParameters in tsconfig.json to catch these issues automatically.
Inconsistent Type Declarations
Mixing implicit types, explicit types, and any creates inconsistency. Establish a standard: explicitly annotate parameters and return types, use const assertions where appropriate, and avoid implicit any types.
TypeScript Code Quality Best Practices
TypeScript Code Quality Best Practices Guide
1. Enable Strict Mode in tsconfig.json
Strict mode enables stricter type checking rules including strictNullChecks, noImplicitAny, strictFunctionTypes, and others. This catches more errors at compile time and prevents runtime bugs. Strict mode is essential for production TypeScript projects.
2. Maintain High Type Coverage in TypeScript Code
Aim for 90%+ type coverage to minimize any usage. Explicit type annotations improve code readability, catch errors during refactoring, and make your code more maintainable. Use this free TypeScript analyzer to measure and track type coverage over time.
3. Keep TypeScript Functions Small and Focused
Keep cyclomatic complexity under 10 and functions under 50 lines of code. Small functions are easier to test, understand, and maintain. Each function should do one thing well, following the Single Responsibility Principle.
4. Use ESLint with @typescript-eslint for Consistency
Enforce style rules and catch errors with ESLint + @typescript-eslint. This ensures consistency across your TypeScript codebase and catches type-unsafe patterns automatically. Integrate into your CI/CD pipeline for every commit.
5. Refactor High Complexity TypeScript Code
Break down complex functions into smaller, testable units. Extract conditional logic into helper functions, use guard clauses to reduce nesting, and apply design patterns where appropriate. Use this analyzer to track improvements.
6. Add Explicit Return Type Annotations
Always annotate return types explicitly instead of relying on inference. This makes function contracts clear, prevents accidental API changes, and helps catch errors during refactoring. It also improves code readability.
7. Use const by Default, Prefer let over var
Modern TypeScript code should use const for immutability by default, let for variables that change, and avoid var entirely. This reduces bugs from accidental mutations and improves code clarity.
FAQ — TypeScript Code Analysis & Metrics
Frequently Asked Questions About TypeScript Code Analysis
The main free TypeScript static analysis tools: ESLint + @typescript-eslint — most widely used, catches type-unsafe patterns and enforces best practices. tsc --strict — the TypeScript compiler itself with strict mode enabled. FTA — Fast TypeScript Analyzer, a Rust CLI tool that measures complexity and maintainability scores across your entire repository. SonarCloud — free tier for public repos with TypeScript-specific rules. This free online TypeScript analyzer — provides instant browser-based metrics with no installation required.
Cyclomatic complexity is a quantitative measure of the number of linearly independent paths through your TypeScript code. Each decision point (if, for, while, case, etc.) increases complexity by 1. A score of 1-5 is simple, 6-10 is moderate, 11-20 is complex and should be refactored, above 20 is a maintainability risk. High cyclomatic complexity makes TypeScript code harder to test, understand, and maintain.
Use this free browser-based TypeScript code analyzer. Simply paste your TypeScript code and click "Analyze TypeScript Code" to instantly get cyclomatic complexity metrics, type coverage score, maintainability grade, and code quality issues. No npm install or configuration required. Perfect for quick code reviews and learning about code metrics.
Key TypeScript code metrics to track: Cyclomatic complexity (number of independent code paths — under 10 per function is ideal), lines of code per file (under 200-300 for maintainability), type coverage percentage (ratio of typed vs any code — aim for 90%+), any type usage count (each any is a type safety hole), function count and average length, and unused variable/import count. These metrics together give a maintainability score.
Over 90% type coverage is excellent, indicating most of your TypeScript code has explicit or inferred types. 70-90% is good but has some type safety gaps. Below 70% means significant use of 'any' type which defeats TypeScript's purpose. Aim to increase type coverage by replacing 'any' with specific types or using 'unknown' with proper type guards.
To improve TypeScript code metrics: Reduce cyclomatic complexity by breaking complex functions into smaller units, increase type coverage by replacing 'any' with specific types, reduce file size by splitting large files into modules, add explicit return type annotations, remove unused variables and imports, enable strict mode in tsconfig.json, and use this free TypeScript analyzer to measure progress over time.
knip is the best dedicated free tool for finding unused TypeScript exports, files, and dependencies across a project. ts-prune finds unused exports. ESLint's no-unused-vars and @typescript-eslint/no-unused-vars catch unused local variables at the file level. TypeScript's own noUnusedLocals and noUnusedParameters compiler flags also detect unused declarations. This free analyzer detects unused variables in the pasted code snippet.
Static code analysis in TypeScript requires three layers: Compiler checks — enable strict: true in tsconfig.json for maximum type safety. Linting — add ESLint with @typescript-eslint/recommended to catch patterns the compiler allows but are considered unsafe. Complexity metrics — use this free tool or FTA to measure cyclomatic complexity and flag files that need refactoring. Run all three in CI/CD to enforce quality on every pull request.
This tool is browser-based for quick code reviews and learning. For CI/CD pipeline integration, use command-line tools: FTA (npm fta-cli) for metrics, ESLint + @typescript-eslint for rule enforcement, or SonarQube for full code quality scanning. These can be integrated into GitHub Actions, GitLab CI, Jenkins, Azure Pipelines, and other CI platforms to automatically check code metrics on every commit.
ESLint + @typescript-eslint enforces coding rules and catches type-unsafe patterns, requiring configuration and installation in your project. This free TypeScript analyzer measures code metrics (complexity, type coverage, maintainability) without enforcing rules. ESLint is for continuous enforcement during development and CI/CD, while this tool is for quick metric analysis and code quality reviews. Both are complementary tools.
TypeScript code quality best practices: 1) Enable strict mode in tsconfig.json, 2) Maintain 90%+ type coverage by avoiding 'any', 3) Keep cyclomatic complexity under 10 per function, 4) Keep functions under 50 lines, 5) Use ESLint with @typescript-eslint, 6) Add explicit return type annotations, 7) Use const by default, prefer let over var, 8) Avoid type assertions (as keyword), 9) Use unknown instead of any, 10) Write unit tests for complex logic.