Is the London underground on today

[ssd]

Or are they on strike

Mostly not. Depends which line you need and where:

tfl.gov.uk/campaign/strikes

Do you mean they are mostly on strike?

Check the TFL website - no strike on tube but as some tube lines and stations are on National Rail lines. But the TFL website will give all the info and you can do journey plan too

Check the TFL app. Some lines are disrupted, but mostly it’s running.