Our O vs 0 checker helps you identify whether characters in your text are the letter O (oh) or the number 0 (zero). The tool analyzes each character and clearly labels whether it’s a letter, number, or special character.
Perfect for debugging code, verifying serial numbers, checking passwords, or any situation where distinguishing between similar-looking characters is critical.
The checker analyzes your text character by character using Unicode values to accurately identify each character type.
Text input Paste or type any text containing characters you want to check. The tool works with any length of text, from a single character to entire paragraphs. You can paste from code editors, documents, or type directly into the field.
Character analysis Each character is examined and classified as either a letter O/o, number 0, other letter, other number, or special character. The tool uses the character’s Unicode code point to make this determination, which is 100% accurate.
Visual display Results are shown in a grid where each character gets its own card displaying the character and its type. Letter O is shown in blue, number 0 in green, and other characters in yellow. This color coding makes it instantly clear which is which.
The checker provides detailed analysis of your text with clear visual feedback.
Letter O (uppercase and lowercase): Identifies both ‘O’ and ‘o’ as letters. These have Unicode values U+004F and U+006F respectively. Commonly confused with number 0 in fonts with poor distinction.
Number 0 (zero): Identifies ‘0’ as a number with Unicode value U+0030. The number zero has a completely different code point than letter O, making them distinct characters despite visual similarity.
Other letters: All other alphabetic characters (A-Z, a-z) are identified and labeled. Helps you understand the full character composition of your text.
Other numbers: Numbers 1-9 are identified separately. Useful for understanding the numeric content of your text.
Special characters: Punctuation, symbols, and other non-alphanumeric characters are labeled as special. Includes characters like -, _, @, #, etc.
Statistics summary: Shows total character count (excluding spaces), count of letter O, and count of number 0. Gives you a quick overview of how many potentially confusing characters are in your text.
This tool is invaluable in many situations where character confusion can cause problems.
Debugging code: When code doesn’t work and you suspect a typo, this tool quickly identifies if you accidentally typed the letter O instead of number 0 or vice versa. A single wrong character can break entire programs.
Password verification: Strong passwords often mix letters and numbers. If a password isn’t working, check if you’re typing O instead of 0. This is one of the most common password entry mistakes.
Serial numbers and product codes: Product keys, license codes, and serial numbers often exclude confusing characters, but when they include both O and 0, this tool verifies which is which.
Data entry validation: When manually entering data from forms or documents, verify that numbers and letters are entered correctly, especially in fields like account numbers or reference codes.
Font testing: Designers and developers can use this tool to test whether their chosen font clearly distinguishes between O and 0. Good fonts make this distinction obvious.
Code example – Python: The string
Password confusion: Password
License key:
Excel formula error:
Use fonts with clear distinction: In code editors and terminals, use monospace fonts like Consolas, Fira Code, or JetBrains Mono that clearly differentiate O and 0. Number 0 typically has a dot or slash through it.
Enable font ligatures: Many modern coding fonts include ligatures that make character distinctions even clearer. Enable these in your code editor settings.
Copy-paste carefully: When copying text from PDFs or images (OCR), always verify O vs 0 characters as OCR software frequently misidentifies these characters.
Use variable naming conventions: In programming, avoid single-letter variables like ‘O’ entirely. Use descriptive names that eliminate ambiguity.
Check important strings: For critical strings like API keys, passwords, and serial numbers, always verify characters with a tool like this before reporting “it doesn’t work.”
Enable character highlighting: Many code editors can highlight similar characters. Enable this feature to catch O/0 confusion during typing.
The visual similarity between letter O and number 0 is a historical artifact from early typewriters and printing, where using the same character for both saved space and complexity. Modern fonts attempt to distinguish them through various means: a slash or dot through zero, different widths, or subtle shape differences.
However, many fonts (especially older system fonts and some web fonts) still make them nearly identical. This is particularly problematic in:
Assuming visual appearance: Don’t trust your eyes alone. Two characters may look identical but have completely different Unicode values. Always verify with a tool when accuracy matters.
OCR errors: Optical Character Recognition software frequently confuses O and 0, especially with poor image quality or unusual fonts. Always verify OCR output for these characters.
Copy-paste from PDFs: PDFs may display O and 0 identically even though they’re different characters. Copying from PDFs is particularly error-prone.
Phone number confusion: Phone numbers never contain the letter O (oh), only number 0 (zero). If someone says “oh” when dictating a number, they mean zero.
Hexadecimal values: In hexadecimal notation, O (oh) is never used – only 0 (zero) and letters A-F. If you see an O in what should be hex code, it’s an error.
Also read: I vs l Character Checker
