CaseConv

Lowercase converter — fold everything down.

The tool opens in lowercase mode. Paste a shouted email, a stray Caps Lock paragraph or a column of mixed-case values and press the button — every capital folds down at once, line breaks intact, and Undo brings the original back untouched.

58 characters49 without spaces10 words1 line

Everyday cases

Developer cases

Everything runs in this tab. Your text is never uploaded, stored or logged.

The tidy direction

Lowercasing is the best-behaved of all the case operations. Where uppercase has a long list of characters that expand — the German ß becoming SS, the typographic ligatures fi and ffl unpacking into two and three letters — the lowercase direction is nearly free of them.

Scanning every code point in the Basic Multilingual Plane through the engine’s own case mapping turns up exactly 1 character whose lowercase form is longer than one character:

The complete set of BMP characters that get longer when lowercased. Measured at build time, not transcribed from a reference.
CharacterCode pointLowercases toCharacters after
İ U+0130 U+0069 U+0307 2

That single entry is the Turkish capital dotted I. Turkish keeps the dot when the letter is capitalised, so folding it back down produces a lowercase i plus a separate combining dot character — visually identical to an ordinary i, but two code points rather than one. If you are comparing strings byte-for-byte after lowercasing, that is the one case that will bite you.

What a round trip destroys

The everyday reason to care about lowercase is that people use it as an undo, and it is not one. Converting up and back down does not return your text; it returns a plausible-looking replacement. Here is what actually happens, measured:

Each string uppercased then lowercased, produced by running it through the tool. “Recovered” means the result is character-for-character identical to the original.
OriginalUppercasedBack downRecovered?What was lost
Straße STRASSE strasse no the ß — it expanded to SS and cannot contract back
NASA NASA nasa no the acronym; nothing marks it as one
iPhone IPHONE iphone no the brand’s internal capital
McDonald MCDONALD mcdonald no the internal capital of a Scots/Irish surname
café CAFÉ café yes nothing — accented letters round-trip cleanly
İstanbul İSTANBUL i̇stanbul no nothing under Turkish rules, but the dot survives as a separate mark

5 of the 6 do not come back. The failures are not exotic — an acronym, a brand name, a surname and a German street. Only the accented word survives cleanly, because an accent is carried through both mappings while a capital is not carried anywhere.

The practical consequence: treat a lowercase conversion as destructive and reach for Undo, which holds the exact text from before each conversion. Reversing the transform is not an option.

Where lowercasing is the right answer

Normalising before you compare

Most real uses of lowercase are not about how text looks but about making two strings comparable. Usernames, tags, spreadsheet keys, product codes and search terms are all commonly folded to lowercase before matching, so that Blue Widget and blue widget count as the same thing. The important discipline is to fold for the comparison and keep the original for display — otherwise the first deduplication run silently rewrites everybody's name.

Rescuing text that arrived in caps

A paragraph pasted out of an old system in full capitals is unreadable and cannot be fixed by re-capitalising it directly, because every word looks equally important. The reliable sequence is: lowercase the whole thing first, then apply sentence case for body text or title case for headings. That two-step is why this tool converts in place, with no separate output box — the second conversion runs on the result of the first.

Slugs, paths and identifiers

Anything destined for a URL, a filename or a config key is conventionally lowercase, because the surrounding systems disagree about case sensitivity. Web servers on Linux treat /About and /about as different pages; the same site on Windows or macOS usually does not. Lowercasing removes the whole class of bug. If you also need the words joined, the developer cases do both in one step.

What lowercase does not touch

Digits, punctuation, whitespace and emoji have no case and pass through unchanged. So do whole writing systems that never developed a case distinction — Chinese, Japanese, Korean, Arabic, Hebrew, Devanagari, Thai. If you paste a bilingual document, only the cased half moves, and that is the correct behaviour and not a gap.

The one language-dependent case is Turkish again, in the other direction: IZMIR lowercases to izmir under English rules and ızmır under Turkish ones, because a Turkish capital I is the dotless letter. Tick Turkish i rules if that is the language you are working in.

Lowercase questions

How do I convert text to lowercase?

Paste it above and press lowercase. Every capital in the block is folded down at once, line breaks kept, and Undo restores the original exactly. It runs entirely in your browser, so it is safe to use on text you would not paste into someone else’s server.

Does lowercase ever change the character count?

Almost never — and that is the asymmetry worth knowing. Scanning the whole Basic Multilingual Plane finds exactly 1 character whose lowercase form is longer than one character: İ (U+0130), the Turkish capital dotted I, which lowercases to an i plus a combining dot. Uppercasing, by contrast, expands dozens of characters.

Will lowercasing and re-capitalising restore my original text?

No. Of the six samples in the table on this page, 5 do not survive a round trip. Case folding is lossy in both directions: nothing in the lowercase string records that “nasa” was an acronym or that “strasse” was “Straße”. Reach for Undo; a second conversion will not do it.

Why would I want lowercase text at all?

Normalising before comparison is the big one — usernames, email addresses, tags, deduplicating a spreadsheet column, or matching search terms. It is also the fastest first step when rescuing text that arrived in full caps: lowercase everything, then apply sentence case or title case to put the capitals back where they belong.

Is lowercase safe for email addresses?

The domain half is genuinely case-insensitive, so lowercasing it is always safe. The local part — everything before the @ — is technically case-sensitive under the email standards, even though in practice virtually every large provider treats it as insensitive. Lowercasing addresses for comparison is normal; permanently rewriting a stored address is a decision and not a formality.

What about text that has no case?

It passes straight through. Chinese, Japanese, Korean, Arabic, Hebrew and Thai have no upper and lower forms, so lowercase leaves them untouched, along with digits, punctuation and emoji. Mixed-script text converts only the parts that have a case.

Keep going

  • All twelve case converters on one page — the full tool, with the four title-case style guides and the six programmer cases side by side.
  • Uppercase Converter — the opposite direction, where the character count can genuinely change.
  • Sentence Case Converter — step two after folding everything down — put one capital back per sentence.
  • Camel Case Converter — lowercase plus joined words, for slugs, keys and identifiers.
  • Word Counter — our sister tool for the other half of the job: word, character and reading-time counts when you are writing to a limit instead of fixing capitalisation.