Uppercase to Lowercase

What the Uppercase to Lowercase Does

Type or paste your text and it comes back entirely in lowercase. Despite the name, it does not only act on uppercase input — it lowercases whatever you give it, leaving already-lowercase letters, numbers and symbols alone.

It is the quick fix for shouty all-caps text, mixed-case input you want flattened, or normalising text before comparing or searching it, where case differences would otherwise get in the way.

How It Works

The tool applies the browser's standard lowercasing, which follows Unicode's default case mappings. That means it correctly lowercases not just A to Z but accented and non-Latin capitals too — É becomes é, Ω becomes ω — using the same rules every modern browser shares.

The mapping is locale-independent, so it gives the same result regardless of your language settings. That is what you want almost everywhere, with one well-known caveat: Turkish and Azerbaijani treat the letter i specially, and the default rule does not match their convention.

Data source & conversion logic

1. Read the text. Take whatever you typed or pasted.
2. Apply Unicode lowercasing. Map every uppercase letter to its lowercase form using the standard case mappings.
3. Leave the rest alone. Digits, punctuation, spacing and already-lowercase letters pass through unchanged.
4. Return the result. Output the fully lowercased text, live as you type.

Worked example

Only letters change case; digits, punctuation and spacing stay the same. Accented capitals lowercase too.

Technical Details

Standards & references

• Unicode case mappings — lowercasing follows the Unicode standard's default mappings, so accented and non-Latin capitals (É, Ω, Я) are lowercased correctly, not just A to Z.
• Locale-independent — the conversion ignores language settings and gives the same result everywhere — the right behaviour for general text.
• Turkish and Azerbaijani i — these languages have a dotted and a dotless i with their own case rules; the default mapping turns the capital I into a plain i, where Turkish would expect the dotless form. It is the one common exception.

Accuracy & Limitations

It is Unicode-aware, so it lowercases far more than A to Z — accented Latin letters, Greek, Cyrillic and more all convert correctly. Scripts without case, such as Chinese or Arabic, pass through unchanged.

The mapping is locale-independent. For almost every language that is exactly right, but Turkish and Azerbaijani are exceptions: their dotted i and dotless i have special rules, so the capital I is lowercased to a plain i rather than the dotless one those languages use.

A few characters have no simple one-to-one lowercase and follow the Unicode default. The German sharp s, for instance, is already lowercase and is left as it is.

It changes case only. It does not strip accents, remove punctuation, trim spaces or otherwise alter the text — lowercasing is the single transformation.

Already-lowercase input is returned unchanged, so running it twice has no further effect. It is safe to apply to mixed-case text.

Real-World Use Cases

When to use it — and when not to

Need to go the other way? Use a lowercase-to-uppercase or general case converter. Want Title Case or sentence case? Use the title-case converter. Need Turkish-correct casing? Use a tool that applies the Turkish locale rule.

Frequently Asked Questions

References

• String.prototype.toLowerCase() (MDN Web Docs)
• String.prototype.toLocaleLowerCase() (MDN Web Docs)
• Letter case (Wikipedia)

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