Sentence Case Converter

This converter rewrites text so each sentence opens with a single capital letter and everything else reads as ordinary lowercase prose. That fits a narrow but common set of needs: calming down text that arrived in ALL CAPS or erratic mixed case, normalising rough notes before they go into a document, and tidying copy pulled from a spreadsheet, form export, or chat log so it reads like sentences rather than shouting.

For web and office work it is useful as a pre-publishing step. Headings, captions, support replies, and body paragraphs that were typed inconsistently can be flattened to one predictable style before you do the manual polish. Students and admin staff can use it to clean dictated or pasted material; for data prep it gives a uniform baseline before further processing.

It is best understood as a normalisation step, not a finishing tool. If your real goal is a polished headline, reach for the Title Case converter instead. Use this when the target is genuinely sentence-style prose and you want one consistent starting point you can then correct by hand.

The interaction is deliberately short. Paste or type your text into the input box and press Run; the result appears in the output panel with live word and character counts so you can confirm nothing was lost. From there you can Copy the result to your clipboard or Download it as a plain .txt file, and a reset clears both panels for the next batch. Everything runs in your browser tab, so nothing is uploaded and nothing is kept once the tab closes.

The conversion first lowercases the entire input, then capitalises the very first letter and the first letter that follows a full stop, question mark, or exclamation mark plus a space. Spacing, line breaks, numbers, punctuation, and symbols are otherwise passed through unchanged, and accented Latin letters are handled by your browser's locale-aware casing.

What it does not do matters just as much. There is no file drop or document import, no batch mode, and the only output is .txt or a clipboard copy. It does not fix grammar, detect proper nouns, or preserve any intentional capitalisation you typed on purpose.

The capitalisation is a heuristic driven by punctuation, so it has predictable blind spots. Because the whole input is lowercased first, names, brands, acronyms, and the pronoun I are all demoted: NASA becomes nasa, London becomes london, and I becomes i. Any of these will need a manual fix afterwards. This is the single most common surprise.

A new sentence is only detected after a period, question mark, or exclamation mark followed by whitespace. Sentences separated only by a line break with no terminal punctuation will not be recapitalised, and a full stop with no following space (as in some run-together text) is skipped too. Abbreviations and decimals such as e.g., Dr., or 3.5 can also trigger an unwanted capital on the next letter.

Avoid pasting content where existing capitalisation is meaningful, such as code, structured identifiers, or text with deliberate styling, since all of it is flattened first. Treat the output as a draft baseline rather than a final result.

Read the output panel against the original and confirm the word and character counts match what you expected, so you know nothing was truncated. Then scan specifically for the heuristic's weak spots: proper nouns, brand names, acronyms, and standalone I that were lowercased, plus any sentence that began after a line break or after an abbreviation or decimal where the capital is wrong or missing.

Pay attention to punctuation edges. Confirm that genuine sentence starts gained a capital and that mid-sentence dots in abbreviations or numbers did not. Restore any intentional styling the lowercasing removed before you publish or share the text.

For anything official, financial, or legal, verify the converted text manually rather than trusting the automatic capitalisation. This tool standardises sentence starts; it does not validate meaning, names, or correctness, so a human read-through remains the deciding check for high-stakes copy.