Catch a config typo
Before
API_TIMEOUT=3000After
API_TIMEOUT=30000One extra zero turns a 3-second timeout into a 30-second one. A diff checker spots this in seconds - eyeballing two .env files often misses it.
Text Compare / Diff Checker
Compare two blocks of text or code side-by-side with line and word diff.
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What is a diff checker?
A diff checker compares two pieces of text or code and highlights what was added, removed, or changed. Developers use diffs constantly: reviewing code, debugging configuration changes, comparing API responses, validating migrations, and understanding edits before committing them.
Reading diffs is a core developer skill. It separates *real behavior changes* from harmless reformatting and helps you spot the one altered character in a 200-line block. Once you internalize the green / red / yellow rhythm, code review becomes much faster.
Two flavors of diff matter most: *line diff* (which lines changed) and *word diff* or *character diff* (what changed inside a line). A good diff tool lets you switch between them depending on whether you're comparing source code or paragraphs of text.
What you'll learn while comparing text
- Line diffs show *where* changes happened. Word and character diffs show *what* changed inside a line.
- Whitespace can be meaningful (Markdown, YAML, Python) or harmless (most other code) - toggle the ignore-whitespace option accordingly.
- A small-looking diff can have huge impact if it changes a value, condition, route, environment variable, or feature flag.
How to compare two texts step by step
Paste the two versions
Drop the original text on the left and the new version on the right. Code, JSON, plain prose, config files - anything works.
Pick line or word diff
Use line diff for source code or structured data. Switch to word diff when comparing paragraphs of text where wording is what matters.
Toggle whitespace and case sensitivity
Enable *ignore whitespace* if you only care about meaningful changes; enable *ignore case* when comparing logs or text where casing is incidental.
Read the colored output
Removed content appears in red on the left; added content appears in green on the right. Modified lines often appear as one of each, side by side.
Iterate
Edit either side and watch the diff update live. This is great for crafting a clean patch before opening a pull request.
Diff colors and symbols quick reference
Conventions used by Coddy's diff checker - and by git diff, GitHub, and most other diff viewers.
| Marker | Meaning | Where it shows up |
|---|---|---|
Red / - | Line removed from the original | Left pane |
Green / + | Line added in the new version | Right pane |
| Yellow / both | Line modified - partial change inside a line | Both panes |
| No color | Unchanged line - common between both versions | Both panes |
@@ ... @@ | Hunk header from git diff - line numbers | Terminal git diff output |
| Word diff | Character or word-level change inside a modified line | Highlighted within a yellow line |
Diff examples to try
Word-level edit
Before
The user can login.
After
The user can log in.
Word diff highlights login → log in. A line diff would just show the whole line as changed; a word diff isolates the actual edit.
Compare two API responses
Response A
{ "id": 42, "status": "draft", "published": false}Response B
{ "id": 42, "status": "published", "published": true}The diff makes it obvious that two related fields changed together. This is the fastest way to verify that a state-changing API call did what it was supposed to.
Compare two versions of a function
Before
function total(items) { let sum = 0; for (const i of items) sum += i.price; return sum;}After
function total(items) { return items.reduce((sum, i) => sum + i.price, 0);}Comparing code online like this is the quickest way to review a refactor: the line diff shows the imperative loop removed and the reduce version added, so you can confirm the behavior is equivalent before committing.
Read a git diff
git diff
@@ -1,4 +1,4 @@ function greet(name) {- return 'Hi ' + name;+ return `Hi ${name}`; }The same color logic powers git diff: lines starting with - (red) are removed, + (green) are added, and @@ ... @@ is the hunk header showing the line range. Paste raw git diff output to read it with syntax-highlighted side-by-side panes.
Common diff mistakes
- Ignoring whitespace when whitespace is significant - Markdown, YAML, and Python all care about indentation.
- Reviewing only the green (added) lines and missing important red (deleted) ones.
- Assuming a clean diff proves the new version is correct. A diff only shows *what changed*, not *whether the change is right*.
Diff Checker FAQ
What is the difference between a text compare and a diff checker?
Nothing - they are two names for the same tool. Both compare two pieces of text and highlight what was added, removed, or modified.
Can I compare code with this tool?
Yes. A text diff works for code, JSON, SQL, Markdown, YAML, config files, and plain text. The line-diff view is especially useful for source code review.
Why do developers use diffs every day?
Diffs power code review, change tracking, regression hunting, and post-incident analysis.
git diff, pull request views, and IDE compare panels are all the same idea.Should whitespace be ignored?
Only when whitespace doesn't matter for the file type. In Python, YAML, and Markdown, whitespace is meaningful and should be compared. In most other code, ignoring whitespace makes diffs cleaner.
Is my data safe in this diff checker?
Yes - the comparison runs entirely in your browser. Your text is not uploaded or stored. Safe to use with internal code, configuration, and customer data examples.
How do I compare code online?
Paste the two versions of your code into the left and right panes and the tool highlights the difference instantly - removed lines in red, added lines in green, and word-level changes inside modified lines. It works for any language (JavaScript, Python, Java, SQL, JSON, YAML) because it compares the text directly. No upload, no sign-up - the comparison runs in your browser.
What is a code diff?
A code diff is the set of changes between two versions of a file - which lines were added, removed, or modified. It's the foundation of version control: every commit, pull request, and code review is read as a diff. This tool shows the same added/removed/changed view as
git diff and GitHub, but for any two snippets you paste, with no repository required.Can I see the difference between two files?
Yes. Open each file, copy its contents into one side of the comparison, and the diff highlights every line that differs. Use line-diff mode for code and structured data, and turn on *ignore whitespace* if formatting-only changes are creating noise you don't care about.
