Requested feature overview description.
The /posts.json API endpoint only allows tags, limit and page.
The proposed blacklist parameter would allow passing a blacklist formatted like the blacklist tags field in the user settings.
That blacklist is then also applied to the query.

Why would it be useful?
It would allow having bots (For example my https://t.me/e621_inline_bot) with custom blacklists that don't need complete access to a user account.

What part(s) of the site page(s) are affected?
https://e621.net/help/api#posts_list
https://e621.net/posts.json
https://e621.net/posts

blacklist is a client-side feature, so your bot should really be applying the blacklist itself against the results it receives.
or you can include it as part of the search query - remember you can have up to 40 terms in one search expression now

Didn't actualy know it is only client side, thx.

How do I "close" feature requests here?