Pluralize / Singularize Tool

How to use

1. 1Pick a direction at the top: Singular to plural turns user into users; Plural to singular turns users into user.
2. 2Type or paste a single word into the input box. The output, the rule used, and the rule color badge update as you type.
3. 3Open Bulk mode to paste a list of words separated by line breaks, commas, spaces, or tabs. The two-column table shows the singular and plural form for every word.
4. 4Use Copy to grab a single result, Copy table to grab the full bulk list as plain text, or Download .tsv to save the bulk results for a spreadsheet.
5. 5Read the rule badges (uncountable, irregular, suffix rule, or default) to see which path produced each answer, and trust your own ear for unusual proper nouns and technical terms.

About this tool

Pluralize / Singularize Tool converts any English word between its singular and plural forms in your browser, using a deterministic three-layer algorithm so every result is explainable. The first layer is a curated set of uncountables: words like sheep, fish, deer, news, software, equipment, and information have the same singular and plural form, so they short-circuit both directions and return the input unchanged. The second layer is a bidirectional table of irregular pairs that no suffix rule can predict: child and children, mouse and mice, person and people, foot and feet, tooth and teeth, ox and oxen, goose and geese, datum and data, criterion and criteria, plus the common compound -man and -woman words like fireman, policeman, and businesswoman. The third layer is an ordered list of suffix rules that mirror the standard English heuristics. Pluralize mode applies these rules in order: -y after a consonant becomes -ies (city to cities, party to parties), -s, -x, -z, -ch, and -sh add -es (box to boxes, watch to watches, wish to wishes), -fe and -f for the classic set become -ves (knife to knives, wolf to wolves), Latin -us becomes -i (cactus to cacti, fungus to fungi, syllabus to syllabi), Greek -sis becomes -ses (analysis to analyses, basis to bases, crisis to crises), Latin -um becomes -a (datum to data, medium to media, bacterium to bacteria), Greek -on becomes -a (criterion to criteria, phenomenon to phenomena), and a conservative -o list adds -es (potato, hero, tomato) while ordinary -o nouns just take -s (photos, pianos). Anything that does not match any rule gets a default +s. Singularize mode reverses every rule in the correct order: -ses before -s, -ves before -s, -ies before -s, and sibilant -es before bare -s, so plurals like boxes, knives, cities, and analyses all return their correct singulars. Capitalization is detected and preserved, so Box becomes Boxes, BOX becomes BOXES, and box becomes boxes. Each result carries a visible rule badge: amber for uncountables, fuchsia for irregulars, emerald for matched suffix rules, and sky for the default fallback, so writers, developers, and learners can see exactly which path produced each answer and decide whether to trust it. A bulk mode accepts a list of words separated by line breaks, commas, spaces, or tabs, builds a two-column singular and plural table for the whole list, and exports the result as a tab-separated values file. Useful for software developers naming database tables (user becomes users, category becomes categories) and API resources, copywriters and content writers checking plurals before publishing, ESL learners practicing irregular plural patterns, brand and product namers checking whether a name pluralizes cleanly, and writers preparing technical or scientific copy that uses Latin and Greek-derived plurals. Word lists run entirely in your browser, so internal naming drafts, glossaries, and unpublished copy stay on your device.

Free to use. Works in your browser. No signup, no login.