Four finite modes · nothing uploaded
Case Converter
Change pasted or typed text to UPPERCASE, lowercase, Title Case, or Sentence case. Compare live counts, protect important terms, then copy or download the result without submitting the draft.
Uppercase and lowercase use the browser's Unicode-aware English-locale case mapping. Title and sentence modes apply the separately documented English-oriented rules below.
01 / Input
Paste or type text
- Characters
- 0
- Words
- 0
- Lines
- 0
Title & sentence options
These controls do not apply to strict upper- or lowercase conversion.
Comma-separated single words, maximum 30. The converter restores the capitalization exactly as entered.
No submission path: the textareas have no field names or form action. This script uses no network request, URL parameter, local storage, session storage, or draft history.
02 / Output
Converted text
The output is editable only by changing the input or options. Use it as a conversion preview, then copy or download the exact visible result.
- Characters
- 0
- Words
- 0
- Lines
- 0
Unicode uppercase mapping with the English locale. Characters in scripts without case remain unchanged.
The useful distinction
Case mapping is mechanical. Editorial casing is judgement.
An uppercase converter and lowercase converter can apply Unicode case mappings to every cased character. A title case converter or sentence case converter must infer roles: which short words should stay lowercase, whether a period ends a sentence, and whether capitals are an acronym or merely shouted text. This page keeps those jobs separate. The mechanical modes are broad Unicode transformations; the editorial modes are finite English heuristics whose rules and failure cases are visible before you rely on them.
One input, four objectives
Uppercase, lowercase, title case, and sentence case compared
The example deliberately includes an all-cap ordinary word and an abbreviation. The likely-acronym option normalizes QUICK because it is longer than four letters, while preserving API in mixed text.
| Mode | Result | Primary use |
|---|---|---|
| Input | the QUICK brown fox: an API guide |
Source text |
| UPPERCASE | THE QUICK BROWN FOX: AN API GUIDE |
All cased characters to uppercase |
| lowercase | the quick brown fox: an api guide |
Normalize all cased characters downward |
| Title Case | The Quick Brown Fox: An API Guide |
English headings under this page's house rules |
| Sentence case | The quick brown fox: an API guide |
English prose with detected sentence starts |
Exact mode contracts
What each case converter changes
UPPERCASE converter
Calls the browser's Unicode-aware uppercase mapping with an English locale on the whole string. Punctuation, whitespace, emoji, numerals, and uncased scripts pass through. A mapping can expand: a single source character does not promise a single output character.
lowercase converter
Uses the corresponding Unicode-aware English-locale lowercase mapping. This is casing, not accent removal, transliteration, spelling correction, or locale detection. Language-specific casing outside English can require a different locale and a human who knows the text.
Title Case converter
Works line by line. It capitalizes the first and last word; capitalizes ordinary words; keeps a declared list of short English function words lowercase; and restarts capitalization after a colon, en dash, or em dash. Hyphens and original spacing remain in place.
Sentence case converter
Starts every physical line as a sentence, lowers ordinary words, then capitalizes the first word after a detected full stop, question mark, or exclamation mark. A small abbreviation rule protects common titles, initials, decimals, and dotted abbreviations from obvious false boundaries.
English house heuristic
How title case is decided
There is no single title-capitalization rule shared by every publisher, newsroom, academic discipline, and interface. This converter uses a compact rule that is easy to inspect and reproduce; it does not claim to implement an unnamed style guide.
- Split only for decisions. Unicode letters, combining marks, and numbers form word tokens; apostrophes can stay inside. The replacement process keeps the punctuation and whitespace that sat between those tokens.
- Capitalize structural positions. The first and last word on each non-empty physical line receive an initial capital. A word after a colon, en dash, or em dash also starts a new title segment.
- Lower selected short words. The list is: a, an, the, and, but, or, nor, for, so, yet, as, at, by, in, of, on, per, to, up, and via. They are lowercased unless a structural-position rule wins.
- Handle capitals cautiously. In otherwise mixed text, a 2–4-letter all-cap token can be kept as a likely acronym. When most words on a line are all caps, that signal is too ambiguous and the line is normalized instead.
- Let explicit terms win. Keep exact words maps a case-insensitive token back to the capitalization you supplied. This is the dependable route for important abbreviations; it is not an automatic database of names or protected styling.
Boundaries, not understanding
How sentence case is decided
The converter does not parse meaning. It scans the visible punctuation between word tokens and applies a conservative English boundary rule. Each physical line begins fresh, which helps lists and pasted captions but may capitalize a line break that was merely visual wrapping in the source.
Usually starts a new sentence
A question mark or exclamation mark closes a sentence. A full stop followed by closing quotation or bracket characters and whitespace usually does too. Multiple terminal marks are treated as one boundary.
Usually stays inside one sentence
A decimal point between digits, a period inside a dotted initialism, and a period after common prefixes such as Dr., Mr., Mrs., Ms., or Prof. do not trigger the next capital.
Still needs review
St. can mean saint, street, or the end of a sentence; etc. can sit before either a continuation or a new sentence. Ellipses, headings without punctuation, quotations, initials, and specialist abbreviations remain genuinely ambiguous without context.
Unicode, not ASCII substitution
Why upper- and lowercase results can change length
Modern text is not a 26-letter lookup table. JavaScript strings use UTF-16, while visible characters may contain one code point, several combining code points, or an emoji sequence joined into one grapheme. Case mapping works on Unicode characters and can produce a different sequence.
Expansion is valid
The English-locale uppercase mapping of straße includes
STRASSE. That makes the output longer even though no content was
submitted, translated, or invented by this page.
Locale matters
Dotted and dotless forms of I have language-specific rules. This page explicitly requests an English locale; it does not guess Turkish, Azerbaijani, Lithuanian, or another language from a pasted paragraph.
Some scripts have no case
Emoji, Han characters, Arabic letters, many symbols, and numerals do not acquire an upper- or lowercase form. They remain in the same order. That is correct case mapping, not evidence that every writing system uses capitalization.
Counts state their unit
The live “Characters” count uses Intl.Segmenter grapheme clusters when
the browser provides it and falls back to Unicode code points. The input limit is
separately enforced on UTF-16 code units, matching the textarea platform limit.
Practical jobs
When a case converter is useful
Cleaning imported text
Normalize a column, copied heading, or all-cap paragraph before editing it. Keep line breaks visible, compare input and output counts, and review the result before replacing a source of record.
Preparing headings and labels
Use Title Case as a transparent first pass when the destination wants prominent word capitals. Compare its short-word list with the actual house style, then check names, abbreviations, and intentional casing manually.
Repairing accidental capitals
Sentence case can turn a mostly uppercase note back into readable prose, but an all-cap source removes evidence about acronyms. Put essential abbreviations in Keep exact words before converting.
Building repeatable examples
The finite rules make the page suitable for examples and QA fixtures where the same browser casing algorithms are available. It is not a replacement for language-aware editorial review or application-specific normalization.
Review before publishing
What this converter cannot infer
- It cannot know whether an uppercase token is an acronym, emphasis, a model number, an ordinary word, or an error. The 2–4-letter rule is only a visible heuristic.
- It cannot identify people, places, scientific notation, source-code identifiers, intentional mixed case, or organization-specific styling from meaning.
- It does not correct spelling, grammar, punctuation, quotation style, whitespace, hyphenation, or line wrapping. It changes casing while preserving intervening text.
- It does not certify compliance with a publisher, institution, legal filing system, or design system. Their documented style and own validation remain authoritative.
- The copy action depends on clipboard permission. The download uses a temporary local Blob URL; neither action creates a server-side archive or recovery copy.
Frequently Asked Questions
- Does this case converter upload or save my text?
- No. Conversion and counting happen inside the current browser tab. This feature has no text submission endpoint, puts no draft in the URL, and uses neither local storage nor session storage.
- What is the difference between title case and sentence case?
- Title case capitalizes most words while keeping a declared set of short English function words lowercase except at important positions. Sentence case capitalizes the beginning of each detected sentence and otherwise lowers ordinary words.
- Will title case preserve acronyms and proper names?
- It can preserve likely two-to-four-letter all-cap abbreviations in mixed-case text, but that is only a heuristic. Add important single-word terms to Keep exact words, then manually review names, specialist notation, and intentional styling.
- Why can uppercase or lowercase change the character count?
- Unicode case mappings are not always one character to one character. For example, an uppercase mapping can expand a lowercase letter into more than one code point, and locale-specific dotted-letter mappings may contain combining marks.
- Which title-case style does this tool follow?
- It uses a documented house heuristic rather than claiming one universal style: first and last words are capitalized; selected short English words stay lowercase; a word after a colon or dash is capitalized. Formal style guides can differ.
- How does the text download work?
- The browser creates a temporary plain-text Blob from the visible output, starts a local download named converted-text.txt, and revokes the temporary object URL. The draft is not sent to this site's server.