Tool Overview

This tool compares two pieces of text and shows exactly how they differ. You paste or upload the original text on one side and the changed text on the other. The checker then runs a word-aware diff and highlights additions and deletions with clear colors. It also calculates summary statistics, lets you copy or download the diff output, and provides an optional smart analysis to help describe the change in plain language.

The problem it solves is finding and understanding changes between document versions, notes, descriptions, or any other text content. Reading two long texts line by line to spot differences is slow and easy to get wrong. This tool shows changes directly, using green for added content and red for removed content, while keeping unchanged parts intact.

The text diff checker is useful for writers, editors, reviewers, students, and developers. A beginner can use it by simply pasting text into both fields and clicking compare. More advanced users can load files, handle long content within safe limits, and export or analyze the diff output for reporting, documentation, or review workflows.

Background & Concept Explanation

A text diff compares an old version of text with a new version and expresses the changes as insertions, deletions, and unchanged segments. Classic line-based diffs work at the level of entire lines, but for many documents, especially prose, a word-level diff is more informative. Word-level diffing groups characters into tokens (such as words and spaces) and marks which tokens were removed or added. A related operation involves comparing files as part of a similar workflow.

This tool uses a word-level diff algorithm that understands spaces. It breaks each text into a sequence of words and spaces, finds matching sequences between the two inputs, and marks the rest as additions or deletions. The result is a list of parts where each part knows whether it was added, removed, or kept. Presented as colored text, these parts make it easy to see which sentences or phrases were introduced or removed.

Comparing text manually is difficult when documents are large or when changes are subtle, such as a few words in a long paragraph. You might miss a small deletion or a slight wording change. The text diff checker removes that uncertainty by systematically computing differences and summarizing them in terms of how many changed blocks there are and how much of the text they affect.

Key Features

• Two text input panels. The interface includes two editors labeled "Original" and "Modified". You can type directly, paste from the clipboard, or load text files. Character counters below each panel help you stay within the allowed length.
• File upload with validation. Each panel has a file upload icon. When you choose a file, the tool checks that its size is at most 5 MB and that it has a text-like extension or MIME type. Unsupported or oversized files trigger an error message and are not loaded into the editor.
• Length safeguards. To keep the browser responsive, the tool enforces a maximum number of characters per field (50,000). Pasted text beyond that limit is blocked, and overlong file content is truncated with a warning that only the first part is used. A colored counter warns you when you are near the limit.
• Word-level diffing. Under the hood, the checker uses a diff library that compares texts with awareness of words and spaces. This means it can highlight individual words that changed, rather than only whole lines. It records each contiguous region of added or removed text as a diff block.
• Change statistics. After computing the diff, the tool counts how many blocks were added and removed, and computes a total number of changed blocks. It also estimates a "sentiment" for the change based on the fraction of the text that was modified, classifying it as "cleanup", "minor", or "major".
• Interactive diff display. The diff result is rendered in a dedicated component. Added parts are generally shown in one color (e.g. green), deleted parts in another (e.g. red), and unchanged text retains the base color. This view is suitable for quick visual scans and detailed review.
• Swap and clear actions. A simple control lets you swap the contents of the two panels. This is helpful when you want to reverse the perspective of the comparison. A clear button empties both text areas and resets diff results and errors.
• Copy diff output. A copy button builds a compact diff text by prefixing added segments with "+", removed segments with "-", and leaving unchanged segments unprefixed. This text is copied into the clipboard so you can paste it into emails, notes, or issue trackers.
• Download diff as text. A download button saves the same compact diff to a file named "text_diff.txt". This file provides a portable diff record that does not depend on the UI.
• AI explanation panel. An optional "Smart Analysis" toggle shows or hides an AI explain panel. When active, the panel can send the original text, modified text, and summary statistics to a backend service and display a plain-language explanation of what changed.
• Error feedback. The tool displays error banners at the top for issues such as missing input, excessive length, unsupported file types, or failures during diff calculation, copy, or download. Each banner can be dismissed after reading.

Common Use Cases

Reviewing document edits. When editing reports, essays, or articles, you can keep a copy of the previous version and run it through the tool together with the latest draft. The diff highlights what was added and removed, helping reviewers focus on new or altered content. For adjacent tasks, viewing code diffs addresses a complementary step.

Checking changes to terms or policies. For contracts, terms of service, or privacy policies, even small textual edits can have large implications. By comparing two versions in the text diff checker, you can see exact wording changes and confirm that no clauses were unintentionally altered or removed.

Detecting subtle changes. Sometimes you receive text, such as code comments or documentation, that has minor modifications that are hard to see by eye. Word-level diff highlights replaced or reordered words and can reveal changes like swapped phrases or fixed typos.

Creating a summary of changes. When you need to explain what is different between two versions of a document, you can use the change statistics and AI explanation (if available). The sentiment metric tells you whether the change is mainly cleanup or a major rewrite, and the AI summary can provide a starting point for a human-friendly description. When working with related formats, comparing XML documents can be a useful part of the process.

How to Use This Tool (Step-by-Step)

1. Open the text diff checker in your browser. You will see two main panels labeled "Original" and "Modified" along with controls for clearing, swapping, copying, downloading, and running comparisons.
2. Paste or type the original text into the "Original" panel. If you want to load from a file, click the upload icon and choose a text-like file. Ensure that the character counter stays within the allowed limit.
3. Paste or type the changed text into the "Modified" panel, or load a second file. Again, watch for length warnings and adjust if necessary.
4. If the texts are reversed, use the swap button between the panels to swap original and modified texts. This does not change the actual diff logic but may make the result easier to interpret.
5. Click the "Compare" button. While the tool is computing, a "Comparing..." state appears and the button is disabled. When complete, the diff result area and summary bar appear below the inputs.
6. Review the summary bar. Note how many blocks were added and removed, the total number of changes, and whether the sentiment is "cleanup", "minor", or "major".
7. Scroll through the diff view to inspect the actual text changes. Look for green segments to see new content and red segments to see removed content. Unchanged text provides context around each change.
8. If you need a compact textual representation of the diff, click the copy button. The tool constructs a diff string with "+" and "-" prefixes and places it on your clipboard. Paste it into your notes or tools as needed.
9. To download a diff file, click the download button. A file named "text_diff.txt" is created that contains the same compact diff.
10. If you want an AI explanation, enable the Smart Analysis toggle and use the AI panel. Wait while it processes the texts and summary and then read the explanation. Use this as an aid when describing changes to others.
11. To start a fresh comparison, click the clear button. This resets both text areas, the diff result, summary, and any active analysis or errors.

Calculations & Logic

The checker first enforces basic type checks: both inputs must be strings. It then temporarily truncates each input to a maximum allowed size for performance while still preserving most content. This truncated text is then passed to the diff algorithm.

The diff algorithm performs a word-level comparison that preserves spaces. It creates a sequence of segments, each with a value and flags indicating whether it was added, removed, or unchanged. Each segment’s value is the actual text (words plus any spaces) for that region. From these segments, the tool calculates how many characters were added and removed by summing their lengths.

To measure the relative size of the change, the tool computes a change ratio: (added characters + removed characters) divided by the maximum length of the two inputs. Based on this ratio, it assigns a sentiment label. High ratios are labeled as "major" changes, medium ratios as "minor", and very small ratios as "cleanup", indicating mostly small tweaks. In some workflows, viewing JSON differences is a relevant follow-up operation.

In addition to raw character counts, the tool counts how many segments are added or removed and how many total segments represent changes (added or removed). These counts form the basis of the summary bar and also help any AI explanation module estimate change complexity.

When building the diff text for copy and download, the tool iterates over the segments and prefixes each segment based on its type. Added segments get a "+", removed segments get a "-", and unchanged segments retain no prefix. The segments’ values are concatenated to produce a single diff string that can be read or processed elsewhere.

If anything goes wrong during diff calculation, such as an exception thrown by the underlying library, the tool logs the error and falls back to a simple diff representation with all content treated as unchanged. It also sets a neutral summary with zero changes and a "cleanup" sentiment, so that the user is not misled by partial results. For related processing needs, reversing text handles a complementary task.

Reference Tables or Scales

These limits help ensure that the UI remains responsive even for large comparisons, while still covering common document and code sizes.

Tips, Limitations & Best Practices

Use the tool for plain text content, such as documentation, logs, simple code snippets, or prose. It is not suited for binary or richly formatted files; those should be converted to text first.

For very large documents, consider comparing sections rather than entire files at once. This helps avoid hitting limits and makes the diff easier to read.

Remember that word-level diff is designed to be human friendly, not machine-precise at the character level. For very fine-grained comparisons, you may still want to use additional tools or highlight characters manually once the broad changes are known.

Be careful when interpreting sentiment. A major sentiment means a large fraction of the text was changed, but does not by itself indicate quality or correctness. Always read the actual diff to understand the nature of changes.

If you run into repeated errors, such as failed file reads or copy operations, check that your browser supports the required features and that your files are valid text. When in doubt, reduce content size or switch from file upload to direct paste, which often surfaces encoding issues earlier.