Keep a rule and its exception together

WHAT YOU WILL BUILD

A repeatable check for evidence lost at chunk boundaries.

A useful chunk contains the evidence needed to answer a question. In this example, the 30-day return window is incomplete without the restriction on opened items. Inspecting chunk length alone would miss that failure.

FOLLOW ALONG

Work through the example.

1. 01

   Read the two policy paragraphs

   Find the returns window and its exception in the sample code. Write down the expected answer to: Can I return an opened item after 10 days? It is not eligible under this example policy.

2. 02

   Run the 40-character baseline

   Download the lab below and run its command. The fixed-size split separates the evidence; its complete-rule check prints false.

3. 03

   Inspect the paragraph split

   The second splitter uses blank lines. Print structured to see the full returns paragraph. Its check prints true because both required statements survive in one chunk.

4. 04

   Test the boundary again

   Change width to 80 and update the baseline assertion to your predicted result. Then add a long paragraph. A production splitter also needs a size limit and a fallback for oversized sections; preserving paragraphs alone is not enough.

THE COMPLETE LAB

Run it locally.

Run this command from the folder containing your downloaded file:

node rag-chunking.mjs

// SaveMyToken local lab. Run with Node.js 22 or newer.
import assert from "node:assert/strict";

const paragraphs = [
  "Returns: Unused items can be returned within 30 days. Opened items are excluded.",
  "Delivery: Standard shipping takes 3 to 5 working days.",
];
const text = paragraphs.join("\n\n");
const width = 40;
const fixed = Array.from({ length: Math.ceil(text.length / width) },
  (_, i) => text.slice(i * width, (i + 1) * width));
const structured = text.split(/\n\n/);
const containsRule = chunk => chunk.includes("Unused items") && chunk.includes("30 days") && chunk.includes("Opened items are excluded");
console.log("Fixed chunks preserve rule:", fixed.some(containsRule));
console.log("Paragraph chunks preserve rule:", structured.some(containsRule));
assert.equal(fixed.some(containsRule), false);
assert.equal(structured.some(containsRule), true);

Expected output for the unchanged example

Fixed chunks preserve rule: false
Paragraph chunks preserve rule: true

The assertions also check the baseline behavior. After changing an input, predict the result and update the relevant assertion.

EXPLAIN WHAT YOU LEARNED

Interview practice

Try answering aloud before opening the reference answer. These are original learning questions, not a record of any employer's interviews.