In shortPaste your Python code and the checker parses it with Python's own compiler, then reports syntax and indentation errors with the exact line, names that are never defined (with "did you mean…?" suggestions), and common bugs like x == 'a' or 'b' or a missing f-string prefix — all in your browser, without running the code.
How to use it
- Paste your code. Paste the Python program (or open the sample with mistakes already in it).
- Press Check code. The checker parses it with Python's own compiler — the code is not run.
- Read the results. Errors stop the program from running; warnings are probably bugs; info items are style tips.
- Jump to the line. Click a line number to highlight it in the editor, fix it and check again.
What the checker finds
| Level | Examples |
|---|---|
| error | SyntaxError (missing colon, unclosed bracket or quote, print "x"), IndentationError, TabError, curly quotes pasted from a document, names that are never defined such as pritn |
| warning | if x == "a" or "b" (always true), a string with {name} but no f prefix, is used to compare numbers or strings, mutable default arguments, code after return, variables called list, str or input |
| info | Unused imports, == None instead of is None, bare except:, very long lines |
The 5 most common Python syntax errors
- Missing colon —
if x > 5must beif x > 5:. Everyif,elif,else,for,while,def,class,tryandwithline ends in a colon. - Indentation — the body of a block must be indented, consistently. Use 4 spaces; never mix tabs and spaces.
- Unclosed brackets — Python often reports the error on the next line, because it's still waiting for the
). Look one line up. - = instead of == —
if x = 5:assigns; comparisons need==. - Curly quotes — “smart quotes” copied from Word or a website are not valid Python. Retype them as
"or'.
Each of these is explained with broken and fixed code in Python syntax errors explained.
How it works
The checker runs inside a real Python 3 interpreter in your browser. It first calls Python's own parser — so a syntax error here is exactly the one Python would raise — then walks the syntax tree looking for names that are never assigned and for well-known bug patterns. Nothing is executed, so it is safe to check code that deletes files or loops forever. To see what the code actually does, step through it in the visualizer.
Python Coding - Learn Python for Android: a real Python 3 interpreter, code editor, 26 example programs and 12 marked exercises.
Frequently asked questions
How do I check Python code for errors online?
Paste it into the checker on this page and press Check code. Syntax errors, undefined names and common bugs are listed with line numbers and fixes.
Does the checker run my code?
No. It only parses and analyses the code, so it's safe for programs that use input(), loop forever or touch files. Use the compiler to run it.
Why does Python report the error on the wrong line?
Usually because a bracket or string opened on an earlier line was never closed, so Python only notices on the next line. Check the line above the one reported.
Is this the same as pylint or flake8?
It's a lighter, beginner-focused check. It catches syntax errors exactly like Python does, plus the mistakes beginners make most, explained in plain English. Professional projects should also use a full linter like Ruff or pylint.
Can it find logic errors?
Some common ones (always-true conditions, missing f-strings, unreachable code). For other logic bugs, run the code in the visualizer and watch the variables change.