Virality Analyzer
A 0-100 score, a per-second retention curve, and the exact fix for your weakest factor.
Free video virality checker
Why did your last video flop?
Paste it. Castle scores it 0 to 100 on the eight things that make people keep watching, and tells you the one fix to make first.
Free account, no card. 3 to 5 minutes. We never keep your video. Or put two videos head-to-head →
Castle is a free video virality checker. Paste a TikTok, Reel or Short and it scores the clip on eight research-backed psychological factors, shows where viewers drop off, and names the first thing to change.
34/100
Weak hook or pacingHook
Emotion
Curiosity gap
Pattern-interrupt
Story pull
Concreteness
Share-worthiness
Useful to viewers
What Castle does
Score, fix, create, launch.
Scoring and diagnosis are live for everyone. The create-and-launch lanes run in Beta, clearly labeled below.
Compare with a competitor
Your video vs theirs, head-to-head. Who hooks better, where attention drops, what to copy.
Simulated viewer panel
A panel of simulated viewers grounded in 1,000,000 real demographic records. Quotes, a score distribution, and a by-region split for every clip.
Geography lens
Score the same clip through 10 markets, from India to Japan, and see where it lands hardest.
Trend tailwind
Matches your clip against public trend signals Castle tracks, refreshed daily. A tailwind helps distribution; it is not a guarantee.
Hook Recommender
Matches your topic to 30 proven hook archetypes, then rewrites your opening line to fit.
Shareable report cards
Send a link. The score, retention curve, and fixes render for anyone, no login required.
Beta
One-click Meta launch
Push the winning creative to Meta as a paused campaign, with us handling the setup.
Managed onboarding for Agency and Enterprise plans.
Beta
AI content-gen
Generate a clip and on-brand copy so you can ship the fix the same day.
Rolling out to paid plans.
What happens when you paste a link.
01
You paste or upload
A YouTube Shorts link, or a TikTok or Reel from your phone. Clips up to 60 seconds; longer videos are scored on their first 60.
02
Castle watches it like a viewer
Every frame, the sound and the words. Densest on the first 3 seconds, where the scroll decision happens.
03
You get the score and the fix
A 0 to 100 score, a second-by-second curve of where attention dies, your weakest factor, and the one change to make first.
The eight things that decide whether a video travels.
Each one comes from published research on why people watch and share. Castle scores all eight and weights them like this. See how scoring works →
occipital active
Hover a factor to light its region.
Hook
Occipital region
18%
Does the first 3 seconds give the brain a reason not to scroll?
Factor 1 of 8Emotion
Limbic region
16%
Strong feeling is what gets shared: awe, anger, laughter.
Factor 2 of 8Curiosity gap
Limbic region
15%
An open question the viewer has to stay to close.
Factor 3 of 8Pattern-interrupt
Frontal region
12%
Cuts, reveals and swerves that re-grab attention when it drifts.
Factor 4 of 8Story pull
Temporal region
12%
Being carried along by a narrative lowers the urge to skip.
Factor 5 of 8Concreteness
Hippocampal region
10%
Specific, vivid detail sticks. Abstraction slides off.
Factor 6 of 8Share-worthiness
Frontal region
9%
Does sharing this make the viewer look good?
Factor 7 of 8Useful to viewers
Temporal region
8%
People pass on what helps someone else.
Factor 8 of 8Four questions before you paste.
Yes, a free one. It takes one click with Google and never asks for a card. Every report you run is saved.
No. Processing is transient. We keep the score and the metrics, never the clip.
3 to 5 minutes. You can leave the tab open or come back later; the report waits for you.
Paste a YouTube link, or upload any clip from TikTok or Instagram. Clips up to 60 seconds are scored in full.
Stop guessing. Score your next video free.
Paste a link. 3 to 5 minutes. You'll know what to fix.