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. References to that project or other third-party products are used only to clarify differences, discuss established file-management concepts, or identify external documentation.
Scope of the service
The website provides an on-demand File Sync tool and Folder Merger. The tools operate on folders a user explicitly selects through compatible browser APIs. They can scan available entries, compare metadata or file contents, prepare a preview, and perform selected operations after approval.
The service is not a background synchronization agent, backup subscription, recovery service, or cloud-storage provider. It does not continue after the browser session ends and does not offer scheduled jobs, persistent sync history, unattended monitoring, locked-file access, or complete operating-system integration.
Risk of file changes and loss
Any operation that writes to a filesystem carries risk. Copying can fail because permission changes, a device disconnects, storage becomes full, a file changes, or the browser or operating system interrupts the job. Replacement can remove a destination version. Mirror mode can permanently remove selected destination-only files without Recycle Bin recovery.
The preview exposes these actions before approval, but it cannot determine whether a destination-only file is obsolete, whether Folder A is authoritative, or which document contains the correct work.
Use disposable test folders until you understand the workflow. Keep separate backups of irreplaceable data, confirm the source and destination, inspect active filters, review every destructive action, and retain original source folders after a merge until the result has been checked.
FreeFileSync.online does not guarantee recovery of overwritten, removed, corrupted, incomplete, or inaccessible files. Cancellation prevents later operations from being scheduled and attempts to abort the current browser write, but changes already completed remain on disk.
Comparison limitations
Fast Compare relies on relative paths, file sizes, and modification times. It can identify likely changes efficiently, but matching metadata does not prove that contents are identical. Different files can share a name, size, or timestamp.
Smart Compare uses metadata first and falls back to exact content reads when size or modification details differ. If corresponding files have matching metadata, Smart Compare can classify them as a likely match without reading every byte. Use Exact Content Compare when byte-level equality is the question that must be answered.
Exact Content Compare reads corresponding files in chunks and returns identical only after the compared bytes match. That result applies to the file data read during the check. It does not establish that the source file is semantically correct, free from pre-existing corruption, readable by its intended application, or protected from future hardware failure.
Optional post-copy verification repeats a content comparison after writing. Verification adds extra reads and can fail independently of the initial copy. A verified result is useful evidence of equality at that time; it is not a substitute for backups, checks of application-level validity, or long-term storage monitoring.
Filesystem and metadata limitations
Standard browser writes do not expose full control over native filesystem metadata. A copied file may receive a new modification time, and the service does not claim to preserve creation time, ownership, permissions, access-control lists, symbolic-link behavior, alternate data streams, compression flags, or every filesystem-specific attribute.
The browser can also limit access to protected directories, network storage, removable media, virtual filesystems, and files held open by other programs. Performance depends on the number and size of entries, storage device, operating system, browser, filters, exact comparison, and verification. No fixed capacity, transfer speed, or completion time is promised.
Concurrent changes and operation reports
Files and folders can be modified by other applications between scanning, preview, and execution. The tool stores observed metadata and rechecks relevant entries before important writes, replacements, and removals. When an expected state no longer matches, the safer result is to skip or fail that operation and ask for a rescan.
These checks reduce stale-plan risk but cannot create one atomic transaction across an entire directory tree. Keep selected folders quiet during a run. Review the final report for completed, verified, skipped, cancelled, and failed items rather than assuming the entire job succeeded because progress reached its end.
Reports are generated locally and can contain file names, paths, actions, and error details. Inspect and redact a report before sending it to another person because it may reveal sensitive information about your folders.
Privacy and external references
Selected file contents and complete directory scans are processed locally for the core tools and are not uploaded to the website server. Normal site resources still load over HTTPS, and hosting infrastructure may process standard connection and request logs. Email correspondence is handled by the mail providers involved. Read the Privacy Policy for details.
The site can link to third-party technical documentation. External pages control their own content, availability, privacy practices, and terms. A link is provided for reference and does not imply endorsement, accuracy, partnership, or responsibility for the external service.
Informational content
Articles and interface guidance provide general technical information. They are not professional legal, compliance, archival, forensic, cybersecurity, or data-recovery advice. Requirements for regulated records, evidence preservation, business continuity, retention, and confidential information vary. Use qualified professional advice and purpose-built systems when those obligations apply.
Examples use simplified folder names and workflows for explanation. They do not guarantee the same result on every browser, storage device, or filesystem. Product behavior is defined by the current application and the permissions available in the user's environment.
Your decision to use the tools
You are responsible for determining whether a browser-based utility is suitable for the files involved. If a folder is your only copy, a destination contains valuable independent changes, or recovery would be difficult, create another backup and verify it before proceeding.
Use of the service is subject to the Terms of Use. Questions about these limitations can be sent through the Contact page.