How to Build a Node.js Invoice Summarization API Using Chat Completions and JSON Output

A structured approach to building a Node.js text summarization API involves counting tokens before processing, splitting long invoices into bounded chunks, and summarizing each chunk into a consistent JSON format. Each chunk prompt extracts fields such as supplier name, invoice number, date, total, and currency, with missing values returned as null rather than guessed. A final combination pass merges structured chunk results using a map-then-reduce pipeline, preserving chunk order and source labels so reviewers can trace outputs back to their origin. The guide warns that latency metrics are visible by default, but extraction quality must be deliberately instrumented, since a fast but incorrect invoice total is more dangerous than a slower, verifiable one. Developers are advised to evaluate model choices against redacted sample invoices for field accuracy and latency, rather than relying on model names from blog posts.