Case Inverter

Paste any text. Every uppercase letter becomes lowercase and every lowercase letter becomes uppercase. Numbers, punctuation, and whitespace pass through unchanged.

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What case inversion does

Case inversion is the simplest of the case-conversion family. Every uppercase letter becomes lowercase. Every lowercase letter becomes uppercase. Digits, punctuation, and whitespace pass through untouched. The Quick Brown Fox becomes tHE qUICK bROWN fOX.

That's the whole transformation. There are no rules, no edge cases, no style guides. The output is deterministic and reversible: invert twice and you get the original back.

When you might want this

Honest answer: rarely. Case inversion is the joke cousin of the case-conversion family. The legitimate use cases are narrow:

Caps Lock recovery. You typed a paragraph with Caps Lock accidentally on, so capitals came out lowercase and lowercase came out capital. Invert the case and the text reads correctly.
Visual emphasis (informal). tHE iNVERSE oF nORMAL cASE works as a stylistic device for casual writing, social media bios, and creative typography. It reads more "ironic" than ALL CAPS shouting.
Encoding obfuscation (toy). A child's first cipher. Reversible, easy to spot, not actually secure.
Testing case-sensitive systems. When debugging code that depends on case sensitivity, invert sample inputs to verify the system catches it.

For the more useful conversions - UPPERCASE, lowercase, Title Case, Sentence case, camelCase, snake_case - use the case converter, which bundles all of them.

How inversion differs from other case ops

The case-conversion family includes about a dozen named operations, and inversion is the simplest: See also: Title Case Converter. See also: Chicago title case.

Case Inverter (this page): swap upper and lower per letter, ignoring word boundaries.
UPPERCASE: every letter becomes uppercase.
lowercase: every letter becomes lowercase.
Title Case: capitalize the first letter of each word; rules vary by style guide.
Sentence case: capitalize the first letter of each sentence and proper nouns.
aLtErNaTiNg CaSe: every other letter is capitalized - a meme/sponge-bob style.
RaNdOm CaSe: each letter is capitalized or lowercased at random.
camelCase / PascalCase: programming identifier conventions; collapse spaces.
snake_case / kebab-case: programming identifier conventions; use underscores or hyphens.

Inversion is unique in that it preserves which letters were uppercase or lowercase originally - the inverse maps unique characters to unique characters, where most case conversions collapse information.

Privacy

Case inversion runs as a one-line transformation in your browser. Nothing leaves the page, nothing is logged, nothing is uploaded. Verify in your browser's network tab: zero requests after page load.

Frequently asked questions

What is case inversion?

Case inversion swaps the case of every letter: uppercase becomes lowercase, lowercase becomes uppercase. Digits, punctuation, and whitespace pass through unchanged. "The Quick Brown Fox" becomes "tHE qUICK bROWN fOX".

Is case inversion reversible?

Yes. Apply the inversion twice and you get the original text back. The operation is its own inverse.

When would I use this?

The most legitimate use is recovering text typed with Caps Lock accidentally on - your capitals came out lowercase and vice versa. Other uses are stylistic (inverse-case bios on social media) or pedagogical (teaching case sensitivity).

Does this work on non-English letters?

For letters with documented uppercase/lowercase pairs (German umlauts, French accents, Cyrillic), yes. For scripts without case distinctions (Chinese, Japanese, Arabic, Hebrew), the characters pass through unchanged.

How is this different from a case converter?

A case converter has multiple modes (UPPERCASE, lowercase, Title Case, Sentence case, camelCase, snake_case). The inverter is a single transformation. For multi-mode conversion, use the case converter.

Does it preserve the original?

Your original text stays in the input box. The output box holds the inverted version. Both are visible at the same time.

Is there a size limit?

No hard limit. The operation is O(n) and runs instantly on texts up to several million characters.

Does the text get uploaded?

No. Every operation runs in your browser. Nothing is uploaded, logged, or persisted.