Rules shared by major English styles
Most headline-style systems capitalize the first and last word, nouns, pronouns, verbs, adjectives, and adverbs. Articles and common coordinating conjunctions are generally lowercase unless they begin or end the title.
The difficult cases are grammatical: a short word may be part of a phrasal verb, while a longer word may function as a preposition. Proper names and brand styling should retain their established capitalization.
- Capitalize the first word after a colon or dash when the style requires it.
- Preserve intentional capitalization in names such as iPhone or eBay.
- Review both parts of a hyphenated compound instead of applying one blanket rule.
Where APA, Chicago, MLA, and AP-style conventions differ
APA capitalizes words of four letters or more in title case. Chicago's current headline style uses grammatical categories and, in its 18th edition, capitalizes longer prepositions while retaining specified lowercase exceptions. MLA uses headline style for English-language titles and sentence style for many non-English titles.
AP guidance is commonly used for news-style headlines and has its own preposition and conjunction decisions. If a publisher, school, or brand provides a house style, that rule takes precedence over a generic converter.
Why automated title case needs a final human pass
Software can identify word position and a list of minor words, but it cannot always infer part of speech or intent. ‘Is’ is a verb and is normally capitalized; ‘to’ may be an infinitive marker; ‘up’ may be a preposition or part of a verb such as ‘Set Up.’
Use the output as a fast first pass. Then verify proper nouns, acronyms, branded casing, quoted text, and any edge case that changes the meaning.