# How I compare two text blocks line by line

A beginner-friendly guide to text diffs, added lines, removed lines, changed lines, config comparison, and review habits.

- Date: 2026-09-27
- URL: https://ilham.dev/posts/how-to-compare-two-text-blocks-line-by-line/
- Markdown: https://ilham.dev/posts/how-to-compare-two-text-blocks-line-by-line/index.md
- Tags: diff, text, debugging, tools
- Reading time: 2 min


A text diff shows what changed between two blocks of text. It is useful for configs, logs, snippets, and documentation.

The [Text Diff](/tools/text-diff/) tool helps me inspect the input and output without writing a one-off script first.

## The simple idea

A text diff shows what changed between two blocks of text. It is useful for configs, logs, snippets, and documentation.

I use it to answer one focused question at a time, then I review the result before using it anywhere important.

## Step 1: Paste the old text on the left

Paste the old text on the left.

## Step 2: Paste the new text on the right

Paste the new text on the right.

## Step 3: Look for removed lines

Look for removed lines.

## Step 4: Look for added lines

Look for added lines.

## Step 5: Review changed lines in context

Review changed lines in context.

## Step 6: Ignore formatting only if whitespace does not matter for that file

Ignore formatting only if whitespace does not matter for that file.

## Step 7: Use the diff to review changes before applying them

Use the diff to review changes before applying them.

## My checklist

Before I trust the result, I check:

- Paste the old text on the left.
- Paste the new text on the right.
- Look for removed lines.
- Look for added lines.
- Review changed lines in context.
- Ignore formatting only if whitespace does not matter for that file.
- Use the diff to review changes before applying them.

The tool makes the mechanical part faster. The decision still belongs to me: is this result correct, safe, and appropriate for the real task?