Filenames are not enough for a safe folder merge
Backups, phone exports and work folders often contain identical content under different names. A filename-only comparison copies renamed duplicates again, while a relative-path-only merge can overwrite a different version without warning.
A useful preflight must answer three questions: which content already exists at the destination, which files exist on only one side, and which matching relative paths contain different bytes.
Filter cheaply, then verify complete content
DUPESPACE groups files by exact byte size, then reads the beginning, middle and end to eliminate obvious mismatches. Only remaining candidates proceed to complete chunked SHA-256 content verification. A sample never decides that two files are equal.
Complete verification runs in a dedicated background worker. Storage still has to read every candidate byte, but controls, progress updates and safe cancellation no longer compete with hashing on the page’s main thread.
Resolve version conflicts before duplicate content
When the same relative path contains different content, compare the dates, sizes and actual purpose before choosing a version. A matching filename is not evidence that an overwrite is safe.
Renamed or moved exact matches can be marked as copies you do not need to transfer again. Incoming-only files are new candidates. Project, application and backup contexts require separate review because identical content may be required on both sides.
The browser creates a merge map, not file changes
The web tool does not upload, overwrite or delete files. Export the CSV as a decision record, then perform the merge with a file manager you trust.
Use the Windows app when you need to organize duplicate copies. It still revalidates the current file state before any action; a browser report is never permission to skip cleanup safeguards.