Free clip boundary checker
Paste your captions and see where a clip could actually start and stop. This runs the same boundary rules Momevera's renderer uses — in your browser, with no account and no upload.
The checker needs nothing from you. It reads the file on your machine and never sends your subtitles anywhere.
Check your own captions
Nothing is uploaded. The file is read and analysed here in your browser, and no request carrying your subtitles is made — not to us, not to anyone. (The page header still checks whether you are signed in, which is the only request this page makes at all.)
What it is looking for
A clip fails at its edges long before it fails in the middle. Four things decide whether a cut is usable, and all four are visible in a transcript without watching a frame.
- A dangling open
- The first line points at something the viewer has not seen — “and then he said”, “so that is why”, “it was insane”. The sentence is fine; it is unusable as an opening, because the thing it refers to is in footage the clip does not contain.
- An ending that is a setup
- A last line that trails off on a conjunction, or asks a question, is a promise the clip does not keep. The resolver treats it as a setup and extends forward a sentence at a time — up to three — until it lands on one that actually ends.
- Real silence, not apparent silence
- Transcribers smear roughly a sixth of a second into each side of a gap, so a raw pause reads longer than it sounded. The threshold here is applied to the pause with that padding removed, which is why a 0.5s gap on screen is often not a silence at all.
- Scaffolding at the front
- “Okay so”, “right, well”, “yeah I mean”. Deliberately a narrow list: “I”, “you” and “no” are words, not scaffolding, and trimming them would cut into the sentence itself.
How to read the result
Each line is one sentence as the resolver segments it, with the flags that would stop a clip using it as an edge. A line can carry more than one, and most lines carry none — the point is not that transcripts are full of problems, it is that the two or three places where a naive cut would land badly are findable in advance.
A line marked dangling open is not a bad sentence, and one marked ends open is not a bad ending. They are bad edges. The same sentence sitting in the middle of a clip is doing its job perfectly.
If you cut by hand, that list is your shortlist of places not to put a boundary. If you would rather not do it by hand, the full rule set is written out here with the actual constants, and Momevera applies all of it automatically to every clip it makes.
Questions, answered
Is anything uploaded?
No. The file is read with the browser's own file reader and analysed in memory on your machine. No request carrying your subtitles is made — there is no API route behind this tool and no account needed. Close the tab and it is gone. To be exact: the page header does check whether you are signed in, which is the only network request the page makes, and it carries nothing of yours.
What file formats work?
SubRip (.srt) and WebVTT (.vtt) — the two formats every captioning tool exports and the two YouTube, Twitch and Kick hand back. You can also paste the text straight in. Cues that are out of order or slightly overlapping are repaired rather than refused.
Is this the same code Momevera actually uses?
Yes, literally the same module. The checker imports lib/local/boundaries.ts, which is what the renderer calls when it decides where a clip starts and stops. A demo version that only approximated the rules would make this page worth nothing, since the whole point is that you can check the claim rather than take it.
What counts as a dangling open?
A line that begins on a word pointing at something the viewer has not seen — 'and then he said', 'so that's why', 'it was insane'. There is nothing wrong with the sentence; it is just unusable as a first line, because the referent is in footage the clip does not include.
Why is a question flagged rather than penalised?
Because a question is excellent at the start and fatal at the end. Opening on one is one of the strongest hooks available; ending on one leaves the viewer waiting for an answer that got cut off. The flag tells you which end you are looking at.
Do I need this if I use Momevera?
No — these rules already run on every clip it makes. This exists so you can see them working before deciding whether that is worth anything to you, and it is useful on its own if you cut by hand.