What is it?
The TypeScript Checker gives you the same type errors as running tsc, with the error code, line and column, without installing anything. The official TypeScript compiler (version 5.6) with the ES2022 and DOM type libraries loads once and then checks your code on your device. It can also show the JavaScript your TypeScript compiles to.
Who is it for?
Developers testing a snippet, students learning types, and anyone reviewing TypeScript on a computer that has no Node.js.
How to use it
- Paste your code into the TypeScript to check box, or tap Try a sample to see how it works.
- The list of problems updates as you type: ✕ marks an error, ! a warning. The line above it sums up, for example “2 errors, 1 warning. Tap Show to jump to the line.”
- Set the options: Strict mode (recommended) is on by default; tick Report unused variables or Show the compiled JavaScript as needed. The compiled code appears under Compiled JavaScript with a Copy JavaScript button.
- Tap Show next to a problem to jump to that line, fix it, and watch the list update. Problems that are not on one line say Whole file. Clear empties the box.
Worked example
Paste let o = { a: 1 }; o.b = 2;. You get TS2339: property “b” does not exist on type { a: number }. Fix it with let o: { a: number; b?: number } = { a: 1 }; and the error goes away. Turn on Show the compiled JavaScript to see the types removed.
Is my code uploaded?
No. The checker is downloaded once from a public download server (jsDelivr or cdnjs) and then runs inside your browser. Your code never leaves your device, so it is safe for work and client projects.
Errors and how to fix them
- “✓ No type errors”: the code type-checks in the chosen mode.
- TS2322: a value has the wrong type for where it is put, for example a string into a number variable.
- TS2339: the property does not exist on that type. Add it to the type or interface first.
- TS7006: a parameter has no type in strict mode. Add one, such as
(price: number). - Warning about an import such as react: package type files are not available here. Paste the types you need into the box, or check the file in your own project.
- “Could not load the TypeScript type library. Check your connection”: the first load is about 3 MB; reconnect and reload.
Open the tool: TypeScript Checker
Still stuck?
Contact support. Tell us which tool or page you were using, what you tapped, what you saw, and your phone or computer and browser (for example: Android phone, Chrome). We reply by email.
Questions, or an error not listed here?
Tell us in the comments: what you were doing, the exact message you saw, and your device and browser. We read every comment and add new fixes to this article.