Ask HN: Do you ask for permissions before putting clients on your landing page?

Yes.

Depending on your agreements contracts with your clients you may not strictly have to but in general it's considered a best practice to do it. Some clients may not want to be listed, not because they are unhappy with your product, but simply because they choose to not be listed anywhere. Other clients maybe happy to be listed. You should always ask otherwise you risk losing the relationship.

If there's an NDA, it's a strict no for sure...but there are times where it's better to show the landing page, maybe the way it will be showcased and then ask if they have a problem with this... or if this needs to be taken down.

Black Hat Answer- Yes,put all your client logos on your website.

White Hat Answer- No, protect your clients in case your services or software could be used as a gateway into your high profile clients.

Would you want someone to use your own brand without your permission?

If they link to my website and it is viewed in a positive way, yes.