大文字と小文字を変換する方法：無料ツール
テキストを大文字、小文字、タイトルケースなどに変換。
Types of case conversion
Most common case conversions:
| Type | Example | Use |
|---|---|---|
| UPPERCASE | HELLO WORLD | Headers, acronyms, emphasis |
| lowercase | hello world | Normalization, programming |
| Title Case | Hello World | Article titles, names |
| Sentence case | Hello world | Normal text, paragraphs |
| camelCase | helloWorld | JavaScript, Java variables |
| snake_case | hello_world | Python, Ruby, SQL |
| kebab-case | hello-world | URLs, CSS, slugs |
Convert text instantly with the NexTools case converter.
How to use the NexTools case converter
With the NexTools converter:
Step 1: Paste your text.
Step 2: Select desired format.
Step 3: Copy the result.
All processing in your browser. For word counting, use the NexTools word counter.
Keyboard shortcuts for changing case
Windows (Word): Select + Shift+F3 — cycles through UPPER, lower, Title.
Mac: Fn+Shift+F3 in Word.
Google Docs: Format → Text → Capitalization.
VS Code: Ctrl+Shift+P → "Transform to Uppercase/Lowercase/Title Case".
Excel: =UPPER(A1), =LOWER(A1), =PROPER(A1).
For quick conversions without opening any app, the NexTools online converter is fastest.
Naming conventions in programming
camelCase (JS, Java, TS): getUserName. First word lowercase, rest capitalized.
PascalCase (classes, React): UserProfile. Every word capitalized.
snake_case (Python, Ruby, SQL): user_name. Lowercase with underscores.
kebab-case (CSS, URLs): main-container. Lowercase with hyphens.
SCREAMING_SNAKE (constants): MAX_RETRIES.
URL slugs should always be kebab-case. Generate with the NexTools slug generator.
Case conversion in different languages: Unicode issues
Turkish: Lowercase "i" becomes "İ" (dotted), not standard "I". This breaks many programs.
German: "ß" (eszett) uppercases to "SS". "straße".toUpperCase() → "STRASSE".
Greek: Accented letters lose accents when uppercased in modern Greek.
NexTools handles Unicode correctly for all 11 supported languages.
Practical use cases: when case conversion matters
1. SEO meta tags: Title tags should use consistent casing.
2. Professional emails: ALL CAPS = shouting. Sentence case is correct.
3. Databases: Normalize: "John DOE", "john doe", "JOHN Doe" should be one record. Convert to lowercase before comparing.
4. CSV/Excel: Inconsistent imports. UPPER/LOWER/PROPER normalizes columns.
5. Slug generation: URLs must be lowercase. Use the slug generator.
Case conversion in code: JavaScript, Python, CSS
JavaScript: "hello".toUpperCase(), "HELLO".toLowerCase()
Python: "hello".upper(), "hello world".title(), "hello world".capitalize()
CSS (visual only): text-transform: uppercase;, lowercase;, capitalize;
CSS tip: If text should always be uppercase (buttons, headers), use CSS text-transform instead of writing "CONTACT" in HTML.
Title Case: correct rules in English vs other languages
English (AP Style): Capitalize all words except articles (a, an, the), short prepositions (in, on, at), conjunctions (and, but, or). First and last always capitalized.
Spanish: Only capitalize first word and proper nouns. "El señor de los anillos" (NOT "El Señor De Los Anillos").
German: All nouns always capitalized.
Common error: Applying English Title Case to other languages.
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What is the fastest way to change case in Word
Select text and press Shift+F3 (Windows) or Fn+Shift+F3 (Mac). Each press cycles through UPPERCASE, lowercase, and Title Case.
What is the difference between camelCase and PascalCase
camelCase starts lowercase (getUserName), PascalCase starts uppercase (UserProfile). In JavaScript, camelCase for variables/functions, PascalCase for classes/React components.
How do I change case in Google Sheets or Excel
=UPPER(A1), =LOWER(A1), =PROPER(A1). Apply formula to column, then paste as values.
Does CSS text-transform change the actual text
No. Only changes visual appearance. Source HTML stays the same. Screen readers read the original text.
How do I convert text to slug (kebab-case) for URLs
Lowercase, replace spaces with hyphens, remove special characters and accents. The NexTools slug generator does this automatically.
Why does case conversion fail with Turkish or German characters
Languages like Turkish have special rules: Turkish 'i' becomes 'İ' (dotted I), not standard 'I'. Use locale-aware functions: str.toLocaleLowerCase('tr-TR').