Kagi (custom) bangs[1] already supports `!cobalt <youtube video>`
I just added !cobalt to my custom bangs as `https://cobalt.meowing.de#%s`, and it works.
Kagi also accepts new public bangs: https://github.com/kagisearch/bangs#contribution-guidelines
Kagi bangs are free for everyone (a subscription is required for custom bangs and regular search).
- Example of how to use Kagi bangs without subscription: https://kagi.com/search?q=!chatgpt+TEST
- https://zbang.leftium.com/ uses Kagi bangs under the hood.
[1]: https://help.kagi.com/kagi/features/bangs.html#custom-bangs