FreeFileSync.online provides independent, browser-based tools for comparing, synchronizing, and merging folders on a device you control. The site is built for people who need a clear, occasional file workflow without creating an account or sending selected file contents to a processing server.
The main Free Online File Sync tool compares two user-selected folders. It can show files that exist on only one side, files that appear newer, files with different contents, identical files, and files excluded by a filter. After comparison, you can prepare an Update Destination, Mirror A to B, or current-state Custom plan. Nothing is changed during the scan or preview. You choose the operations before the browser writes to either folder.
The Free Online Folder Merger solves a different problem. It combines files from two or more source folders into one destination. You can preserve nested directory structure or flatten included files into the destination root. When several files target the same destination path, the preview can distinguish identical content from a real conflict and apply Keep Both, Skip, Replace, or Replace Only If Different.
A local-first browser workflow
The tools use browser file-system capabilities to work with folders you explicitly select. Folder contents are scanned in the browser, and approved file operations are performed through the permissions provided by the browser. Selected file contents and complete folder listings are not uploaded to the FreeFileSync.online server for synchronization or merging.
This access is intentionally limited. The site cannot silently browse a computer, discover arbitrary folders, or continue working after the tab closes. The operating system and browser remain part of the security boundary. You can cancel a folder picker, deny write access, close the tab, or choose different folders.
Normal website resources still travel over the internet. The browser must request the page, styles, scripts, local font files, and images from the hosting service. That ordinary website traffic is separate from processing the folders selected for a file operation.
Preview before modification
The central safety principle is simple: preview first, approve second, modify files last.
A comparison or merge scan creates a plan without writing files. The preview shows source and destination paths, operation types, file sizes, conflict reasons, and selection controls. Replacement and deletion actions are identified before approval. Mirror removals receive an additional warning because destination-only files can be permanently removed without Recycle Bin recovery.
The tools also recheck important file details before writing. If a source or expected destination changes after preview, that operation is reported as a failure instead of silently applying an outdated plan. Optional exact verification reads the copied source and destination after a write and confirms whether their bytes match.
These safeguards reduce avoidable mistakes, but no browser tool can understand the human meaning of every file. It cannot decide whether a newer document is the correct version, whether a source file was already corrupted, or whether a destination-only file is an intentional archive. You remain responsible for reviewing the plan and keeping separate backups of important data.
Browser support and practical limits
Direct directory selection and writable folder access depend on the File System Access API, a secure context, browser permissions, the operating system, and the selected storage device. Current desktop Chrome, Edge, and compatible Chromium browsers provide the intended experience. When required capabilities are unavailable, the site shows a compatibility notice instead of presenting upload controls that cannot perform the promised local workflow.
FreeFileSync.online is an on-demand utility. It does not provide background monitoring, scheduled jobs, a persistent synchronization database, historical two-way change detection, cloud-drive connections, locked-file copying, or full native metadata preservation. Browser-created copies may receive different timestamps, and the site does not claim to preserve creation times, permissions, symbolic links, or every filesystem-specific attribute.
Independent product and editorial purpose
FreeFileSync.online is an independent browser-based file utility. It is not affiliated with, endorsed by, sponsored by, or an official web edition of the FreeFileSync desktop software project. The name identifies this website and its browser workflow; it does not imply shared ownership or development.
The Blog contains practical guides about folder comparison, updates, mirrors, verification, structure preservation, duplicate detection, and filename conflicts. These articles explain both useful workflows and their limits. Technical references are included selectively where they help readers understand browser APIs or distinguish browser behavior from desktop software.
The project does not require accounts, subscriptions, paid APIs, or a remote file-processing service. It does not include advertising; limited site-usage measurement is described in the Privacy Policy. Questions, corrections, and problem reports can be sent through the Contact page.