Stop letting LLMs hallucinate dates — a tool for AI agents

If you're building an AI agent that touches dates — booking flows, scheduling bots, "remind me on Friday" assistants — you've probably noticed: LLMs are terrible at dates. They hallucinate weekday-to-date mappings. They fencepost-error ranges. They forget what "next Friday" means in Ukrainian vs English. Asking the model to "be careful" doesn't fix it — what fixes it is moving date interpretation out of the model and into a deterministic tool. That's what whenis is. Use it as an agent tool Define a resolveDate(expression, reference) tool that calls whenis . Let the model invoke it instead of guessing. import { createParser } from ' @whenis/core ' ; import { uk } from ' @whenis/locale-uk ' ; import { booking } from ' @whenis/booking ' ; const parser = createParser ({ locales : [ uk ], plugins : [ booking ], options : { preferFuture : true }, }); const ref = new Date ( ' 2026-05-28 ' ); parser . parse ( " наступної п'ятниці " , { reference : ref }); // → { type: 'date', date: '2026-06-05', confidence: 1 } parser . parse ( ' з 5 по 10 червня ' , { reference : ref }); // → { type: 'range', start: '2026-06-05', end: '2026-06-11', nights: 6 } parser . parse ( ' після свят ' , { reference : ref }); // → { type: 'fuzzy', reason: 'holiday_ref', // metadata: { suggest_next_month: true } } English works the same way: import { en } from ' @whenis/locale-en ' ; const parser = createParser ({ locales : [ en ], options : { preferFuture : true } }); parser . parse ( ' next Friday ' , { reference : new Date ( ' 2026-05-28 ' ) }); // → { type: 'date', date: '2026-06-05', confidence: 1 } How it differs from chrono-node Multi-candidate output. A bare "Friday" mid-week emits both this Friday and next Friday with confidence scores. Your agent re-ranks using conversation context — no silent guessing inside the library. Locale as data. Adding RU/PL/CS is one source file with no engine changes. The Ukrainian locale ships full inflection: months × 7 cases, weekdays × 4 cases, pointers, conne