Text Analysis Without a Backend: Replacing an LLM Call With Intl.Segmenter and 60 Lines of JavaScript

Last spring, I had six small text features to build: flag filler phrases in a draft, score sentence-length variation, format a citation, check a document against a rubric. My first design put all six behind an API route that called a model. It worked in an afternoon.

Then I priced it. Anthropic lists Claude Fable 5 at $10 per million input tokens and $50 per million output. A 700-word draft plus instructions runs about 1,500 input tokens, and users hit the button five or six times per session while they edit. The bill is survivable. The rest of the tradeoff is not.