Case Inverter Tool

Swap the case of every letter — uppercase becomes lowercase and vice versa — in seconds, for cleaner copy, quick edits and instant text formatting fixes. Paste the text or drop a file, and the result comes back with the structure of the original completely intact: line breaks, spacing, numbers, punctuation and emoji all pass through exactly as they arrived.

• Swap case — every letter flips to its opposite: uppercase to lowercase, lowercase to uppercase.
• Structure preserved — spaces, tabs, line breaks and blank lines come back byte for byte.
• Non-letters untouched — digits, punctuation, symbols and emoji have no case, so they are copied verbatim.
• Whole characters, not storage units — letters that need two units of storage are read as one letter, which is why they actually invert.
• Live counts — characters, words and lines update as you type, before you commit to anything.

Invert versus the alternating modes

The three modes on this page all work letter by letter, and the difference is what they read. Invert reads your original casing and flips it, so an already mixed-case string stays mixed and simply reverses. The two alternating modes ignore what you typed entirely and impose a pattern — aLtErNaTiNg starts lowercase, AlTeRnAtInG starts uppercase — flipping at every character position, including spaces and punctuation, which is what keeps the pattern aligned across word boundaries.

Case tools are easy to confuse because their names describe the output rather than the operation. This table is the whole family, applied to one string, so you can pick by looking rather than by guessing.

When a different tool is the right one

If you need a fixed target casing rather than a flip — UPPERCASE, lowercase, Title Case, Sentence case, camelCase, PascalCase, snake_case or kebab-case — the Case converter is the page for it. Inverting is specifically the operation that has no target: it depends entirely on what you started with, which is why applying it twice normally returns you to where you began.

Case is not a universal property of writing. Roughly a dozen of the world's scripts distinguish uppercase from lowercase; most do not, and a tool that pretends otherwise either mangles text or silently does nothing to it. Here is exactly what this tool does with each family.

Scripts with no case at all

About half the text on the web is written in scripts that have no notion of upper and lower case. Inverting a page of Arabic, Hebrew, Chinese, Japanese, Korean, Thai or Hindi is not an error and does not fail — it simply returns the text you gave it, and the change summary will report every character as unchanged. That is the correct answer, and seeing it in the summary is how you can tell the tool read your text rather than ignored it.

Greek and the final sigma

Greek writes its lowercase sigma two ways: ς at the end of a word, σ everywhere else. Both are the same letter and both uppercase to Σ, so lowercasing a capital sigma requires knowing where in the word it sits. Inverting ΟΔΟΣ therefore gives οδός's ending — οδος — not οδοσ, which is what a tool that looks at one character at a time produces. It is a small point that anyone reading Greek notices immediately, and it means inverting Greek twice returns the original text rather than a subtly misspelled version of it.

A few letters have no single-character uppercase form. Unicode's default rule expands them, which is correct but not reversible: the text gets longer and inverting a second time cannot recover what you started with. The tool follows the standard by default and offers a way out.

Length preservation, and when to use it

Turn on length preservation and the tool leaves those characters exactly as they are instead of expanding them. Straße becomes sTRAßE rather than sTRASSE, the text stays the same length, and inverting twice returns precisely what you started with. Leave it off when you want Unicode's standard behaviour — which is what you want for anything that will be read as German prose, since ß has no uppercase form in ordinary typesetting. Turn it on whenever the round trip matters more than the typography: comparing two versions of a file, generating test fixtures, or checking a case-insensitive lookup.

Four settings, all free, all of which change the result rather than the packaging. The change summary underneath the result reports what each one actually did, so none of them is a promise you have to take on trust.

• Leave ALL-CAPS words alone — any word that is entirely uppercase and at least two letters long is copied verbatim. Two letters, not one, so I and A stay ordinary words.
• Protect list — exact terms, one per line, left untouched wherever they appear. Case-sensitive, because an exact spelling is the whole point.
• Preserve length — refuse the expansions above so the transform stays reversible.
• Restart per line — alternating modes only — begin the pattern again at every line break.

Protecting brand names and identifiers

Inverting a paragraph of prose is rarely a clean operation, because prose contains words whose capitalization is not a style choice. iPhone, eBay, macOS, JavaScript, a product name, a person's surname, a variable called userId — each of these means something specific in the shape it is written, and flipping it produces a word that is merely wrong. Put those terms in the protect list, one per line, and every occurrence is copied through exactly as written while everything around them inverts normally. This is the setting that makes the tool usable on real documents rather than on test strings.

Leaving acronyms alone

The acronym guard is the broad version of the same idea and needs no list. It looks for words written entirely in capitals — NASA, USA, HTTP2, PDF, CSV — and leaves them as they are. It requires at least two cased letters so that a lone I or A is treated as an ordinary word rather than an abbreviation, and it counts digits and underscores as part of the word so identifiers like HTTP2 and MAX_SIZE survive intact. Combine it with the protect list when a document has both shouty abbreviations and mixed-case product names.

Whenever you need the opposite-case version of some plain text, or the alternating pattern, and retyping it would be slower than pasting it.

Everyday editing

• Caps Lock accidents — a paragraph typed with Caps Lock on comes back correct in one pass, because the shift key was doing the right thing the whole time.
• Pasted headings — a heading copied from a document in SHOUTING CAPS becomes readable immediately.
• Memes and social posts — aLtErNaTiNg cAsE is the mocking-text convention, and both directions are here.
• Proofreading — flipping a line makes casing mistakes visually obvious in a way rereading it does not.
• Any time swapping is faster than retyping — which, past about a sentence, it always is.

Developer use cases

• Case-sensitivity tests — generate mixed-case variants of an input and check that a login, a search or an API route treats them the way you intended.
• Fixture generation — produce opposite-case copies of test data without hand-editing them, and use length preservation so the pair stays byte-comparable.
• Unicode checks — the Greek, Cherokee and Deseret samples on this page are a quick way to find out whether your own pipeline handles case outside the Latin alphabet.
• Log and CSV inspection — drop a .log, .csv or .tsv file straight in; the delimiters and structure are untouched because they have no case.
• Subtitle files — .srt and .vtt are accepted, and the timestamps come through unchanged for the same reason.

Four habits that make the result something you can paste straight back where it came from.

Quality considerations

• Read the change summary before you copy. If the numbers are not roughly what you expected, a setting is doing more or less than you thought.
• Turn on the acronym guard before inverting prose. It is almost always what you want and it costs nothing to check afterwards.
• Try a short sample before committing a long document, especially with the protect list, where a term that also appears inside a longer word will match there too.
• For code and identifiers, review the output — meaning frequently depends on case, and the tool cannot know which of your words are names.
• Use Swap to feed the result back in as input; if inverting twice does not return your original, a length-changing character is the reason, and preserving length fixes it.

When not to use the inverter

• When exact capitalization must be preserved for legal or trademark reasons — protect those terms explicitly rather than trusting a general pass.
• When you want a specific target casing. Title case, sentence case and the programming cases are a different operation; use the Case converter.
• For passwords, keys or secrets, if your organization's policy forbids pasting them into any tool. Nothing is uploaded here, but a policy is a policy.
• For Turkish, where the dotted and dotless i follow language-specific rules that the default Unicode mapping does not reproduce.

It all runs on your device, not our servers. There is no upload step, no server round trip and nothing stored — the transformation happens where you are sitting, which is why it starts the moment you press the button rather than after a wait.

• Free — one document at a time, up to 25 MB. Every option that decides the result is included.
• Pro — up to 20 documents at once, up to whatever your device can handle, delivered as a single ZIP.
• Formats — .txt, .md, .log, .csv, .tsv, .json, .xml, .yaml, .sql, .ini, .srt and .vtt, plus anything you paste.
• Encodings — UTF-8, UTF-16 with a byte-order mark, and the common single-byte Western encodings, detected automatically.
• Anything larger — split the file first and process the pieces — the Text splitter is free and linked below.

A 25 MB document is re-cased in well under half a second on a modern laptop, and the page stays responsive the whole time — you can keep typing while it runs.

• Case converter

  UPPERCASE, lowercase, Title Case, camelCase, snake_case and kebab-case.

• Text reverser

  Reverse characters, words or lines instead of their case.

• Word counter

  Words, characters and reading time for the text you just re-cased.

• Text analyzer

  Readability, frequency and structure for a whole document.

• Text splitter

  Break a file that is over the size limit into pieces first.

• Text merger

  Join the pieces back together after processing them.