Text Case Converter — Uppercase, camelCase, snake_case, and more

1. What does this tool do

This free online text case converter converts text case in one click—uppercase, lowercase, title case, camelCase, snake_case, kebab-case, and more. Use it for convert to uppercase, convert to lowercase, title case converter, or camelCase converter for headings, variable names, and normalising data. No sign-up, no upload; everything runs in your browser. The tool uses regex for matching only and then applies case presets to each match, so you can change the whole text or just specific parts.

2. How to use it

Quick start — presets only: Paste your text, then click the All text preset. That adds a rule that matches the entire input; choose the case style (UPPERCASE, lowercase, camelCase, etc.) in the rule's dropdown.

Selective regex rules

1. Enter text — Paste or type the text to process.
2. Add rules or click presets — Click a preset (for acronyms, emails, words, ALL text, etc.) or add your own pattern. Each rule has:
   • A regex pattern that decides what to match.
   • A case preset (UPPERCASE, lowercase, Title Case, camelCase, snake_case, etc.) that is applied to each match.
3. Set flags — Use the g, i, m, s checkboxes to control matching behaviour.
4. Live vs manual apply — Leave Live preview on to update as you type, or turn it off and click Apply now when you are ready.
5. Copy result — Copy from the Output panel when you are happy with the result.

3. How it works

The tool always runs in a single regex-based mode:

• Regex for matching only — Each rule provides a pattern that selects text to transform.
• Case presets for transformation — For each match, a selected case preset is applied (uppercase, lowercase, title, sentence, camelCase, PascalCase, snake_case, kebab-case, CONSTANT_CASE).
• Whole-text preset — The "All text" preset uses a regex that matches the entire input; choose the case style per rule.
• How rules are applied — You can choose Chain (default), Override, or First match. Chain: rules run sequentially (output of rule N → input of rule N+1). Override: each rule runs on the original text; overlapping regions resolved by the last rule. First match: each rule runs on the original text; overlapping regions resolved by the first rule. On the first error, processing stops and the failing rule is highlighted.

All processing runs client-side in your browser. No data is sent to any server.

4. Use cases & examples

• Format headings — Convert MY HEADING → My Heading (title case).
• Variable names — Convert my variable name → myVariableName (camelCase) or my_variable_name (snake_case).
• Constants — Convert api key → API_KEY.
• Selective uppercase — Pattern \b[A-Z]{2,}\b with uppercase: keep acronyms like "HTML" and "API" in caps.
• Sentence case — Capitalise only the first letter of each sentence.
• Normalise data — Convert column headers or identifiers to a standard format.
• Whole-text preset — Use the "All text" preset to transform the entire text; pick the case style (UPPERCASE, lowercase, camelCase, etc.) in the rule.

Example

• Pattern \b\w+\b with title case → Capitalise every word.
• Rule 1: \b[A-Z]{2,}\b UPPERCASE; Rule 2: \b[a-zA-Z]+\b lowercase → Keep acronyms, lower the rest.

5. Limitations & known constraints

• Pattern validated first — Invalid regex shows an error; no transformation is run.
• ReDoS — Complex patterns on very long text may be slow; avoid catastrophic backtracking.
• JavaScript regex — Uses JS regex flavour; some PCRE features may differ.
• Identifier parsing — camelCase/snake_case assumes words are separated by spaces, hyphens, or underscores; mixed styles may produce unexpected results.
• Unicode — Case conversion uses JavaScript’s built-in methods; some locales may behave differently.