Free Subtitle Encoding Checker

    Scans every cue for the character classes that actually break subtitle rendering: raw control characters, unpaired UTF-16 surrogates, invisible zero-width and bidi-control characters, private-use glyphs that show up as a missing-character box, and the replacement character that means the source file's encoding was already wrong before this tool ever saw it. Harmless ones are stripped in a cleaned download; the ones that mean data is already lost are flagged, not silently deleted.

    • No uploadRuns on your device
    • No accountNothing to sign up for
    • No watermarkYour file, untouched
    • Works offlineDisconnect and try it

    More subtitles tools

    Your files never leave your device

    This is not a promise about how carefully we handle your upload. There is no upload. The file you choose is read into memory by your own browser, processed there, and handed back as a download — the tool has no server component and makes no network request with your data.

    • Nothing is stored. We never receive the file, so there is no copy to retain, no retention period to disclose, and nothing to delete on request.
    • Nothing is transmitted. No upload endpoint, no analytics payload carrying file contents, no third-party processor.
    • You can verify it. Load this page, disconnect from the internet, and use the tool. It still works, because everything it needs is already on your machine.
    • Nothing persists after you close the tab. Files are held in page memory only — not in local storage, not in a cache, not in a database.

    A note on wording, because it matters: we do not describe these tools as “encrypted.” Encryption protects data that travels to somebody else's computer. Your file does not travel, so there is nothing to encrypt and nothing to intercept — which is a stronger guarantee than encryption, not a weaker one. The page itself is served over HTTPS like the rest of the site.

    This makes the tools safe for material you are contractually barred from uploading to third-party services — client footage under NDA, unreleased campaign assets, anything covered by a confidentiality clause.

    Questions

    It flagged a replacement character — can this tool fix it?

    No, and it says so rather than pretending to. A replacement character means the original bytes couldn't be decoded as UTF-8 at all — the real character is already gone by the time this tool sees the text. The fix is re-exporting or re-saving the source file as UTF-8, not editing the damaged copy.

    Why does the cleaned download still contain private-use characters?

    Because they aren't always a mistake. Some authoring tools use the private-use area deliberately for a custom icon or symbol, so removing them automatically could delete something intentional. They're flagged so you can judge each one, rather than stripped on the assumption they're always wrong.

    Do my files get uploaded anywhere?

    No. This tool runs entirely in your browser using the Canvas and File APIs. The file you choose is read into memory on your own machine, processed there, and offered back as a download. Nothing is sent to a server, which is also why it keeps working with your network off.

    Is it actually free, or is there a catch?

    Actually free, with no account and no limit, because it costs nothing to run — the work happens on your device rather than on our hardware. That is different from generating with an AI model on Versely, which does cost credits; there is no free tier for generation.

    These rearrange files. Versely makes new ones.

    Everything on this page works on a file you already have, which is why it costs nothing. Generating something that did not exist — video from a prompt, a voice, a score — runs a model, and that costs credits.