Home › Blog › How to Compare Two Folders Online

Published August 29, 2026 · updated September 7, 2026  ·  6 min read

A folder comparison answers two questions: which paths exist on only one side, and which files at matching paths contain different bytes? A browser tool is useful when you need that answer quickly without installing a desktop application or uploading a project archive.

When a Folder Diff Helps

• Review two exported versions of a project or static website
• Check a deployment bundle against the files you expected to ship
• Inspect a backup before deciding whether it can replace a current copy
• Compare generated output before and after a dependency or build change
• Find configuration drift between two environments

How to Compare the Folders

1. Open the DiffPeek Folder Diff Checker.
2. Choose or drag the original folder into the left zone.
3. Choose or drag the changed folder into the right zone. Dragging is the reliable option for a completely empty directory because a file picker has no file to return.
4. Select Find Differences. Progress remains visible and a long comparison can be cancelled without losing the selected folders.
5. Use the status filter and path search to narrow the result tree, then select a file to inspect it.

Understanding the Results

• Added — the relative path exists only in the changed folder.
• Modified — the path exists on both sides but the byte content differs.
• Deleted — the relative path exists only in the original folder.
• Renamed — an added and deleted file have the same size and full-content hash.
• Incomplete — one or both files could not be fully read, so DiffPeek does not guess whether they match.
• Unchanged — both files have the same path and byte content.

Rename detection finds identical-content moves; it does not treat an edited-and-renamed file as the same historical file. If several added and deleted files share identical content, the deterministic path pairing is only one possible mapping. Turn rename detection off when separate added/deleted entries are more useful.

Reproduce the Release Sample

Choose Try a sample comparison on the folder tool, or open the preloaded release demo. It constructs two synthetic releases in memory with the default dist/** ignore rule and content-based rename detection enabled.

• 1 added: CHANGELOG.md
• 1 deleted: README.md
• 3 modified: a source edit, a same-size MODE=blue → MODE=gold edit, and a same-size binary change
• 1 renamed: notes/todo.txt → notes/tasks.txt with identical content
• 1 unchanged file: src/settings.json
• Excluded: the changed generated dist/bundle.js path; excluded means it was not compared

The repository also includes matching selectable folder fixtures and an expected-results README under tests/fixtures/folder-demo/; the in-product demo is the public, installation-free reproduction.

How DiffPeek Checks Content

The browser supplies relative paths and file handles after you choose a directory. DiffPeek first matches those relative paths. Different file sizes can be classified immediately. Files with the same size are read locally in small chunks and hashed so identical timestamps cannot hide a content change.

The selected bytes, filenames, and paths are processed in the tab and are not uploaded to DiffPeek. Optional product analytics are off until you allow them and are limited to the aggregate values described in the Privacy Policy.

Previewing and Exporting Results

Text files open in a side-by-side line diff with changed characters highlighted. Automatic previews pause above 2 MB, and previews above 20 MB stay disabled to protect tab responsiveness. Binary files are still compared byte-for-byte, but the viewer shows type, size, and modified-time metadata instead of rendering arbitrary bytes as text.

The result tree remains available on narrow screens, supports keyboard navigation, and can be searched by relative path. The locally downloaded JSON report includes a generation time, both folder names, status totals, ignored-path count, up to 50 comparison warnings, relative and previous paths, item type, status/reason/error, and original/changed byte sizes. It deliberately excludes file contents and hashes.

Know the Limits

• DiffPeek reports differences; it does not merge, copy, delete, or synchronise files.
• Browser directory APIs do not expose every filesystem feature, such as permissions, ownership, or reliable symbolic-link information.
• Very large trees take time because accurate content comparison must read the files.
• A successful match is useful evidence, but it is not a substitute for a tested backup and restore process.