Is
Type check values with ease.
Pricing
Free tier
Flat rate
Adoption
→StableLicense
Open Source
Data freshness
Aging · Jun 8, 2026Overview
What is Is?
A utility for type checking values in JavaScript and TypeScript. It simplifies the process of verifying types, making it easier to write robust code that handles different data types gracefully.
Key differentiator
“Provides a lightweight and reliable way to check types in JavaScript and TypeScript, making it easier for developers to write robust code without the overhead of more complex solutions.”
Capability profile
Capability Radar
Honest assessment
Strengths & Weaknesses
↑ Strengths
↓ Weaknesses
@sindresorhus/is primarily supports basic types and does not handle more complex type structures or custom objects well.
The tool returns boolean values for type checks without providing context on why a check failed, which can complicate debugging.
@sindresorhus/is lacks native support for newer or less common types like symbols and maps without additional configuration.
Fit analysis
Who is it for?
✓ Best for
JavaScript and TypeScript developers who need a reliable way to check types in their applications.
Projects that require robust input validation for functions or APIs.
✕ Not a fit for
Scenarios where complex type checking is required beyond basic data types.
Use cases requiring real-time type inference or dynamic typing capabilities.
Cost structure
Pricing
Free Tier
Available
Open source — free to use
Starts at
$0
Model
Flat rate
Enterprise
None
Performance benchmarks
How Fast Is It?
Ecosystem
Relationships
Works well with
Integrations
Next step
Get Started with Is
Step-by-step setup guide with code examples and common gotchas.