I've written a userscript that adds autocomplete functionality to the "Enter new tags" field on galleries. I've only tested it in Firefox with Greasemonkey, but it might work in other browsers, too.
How to use:
- Visit gallery page.
- Type comma-separated list of tags as usual.
- As soon as you've typed 2 or more characters of a tag, a list with tag suggestions will appear under the input field.
- Keep adding or deleting characters to refine the search.
- To accept one of the suggestions from the list, click on it with the left mouse button.
- Alternatively, press the Down arrow key to activate keyboard selection, then use the Up/Down keys to select an entry and press Enter to accept it.
- Accepting a suggestion (either by mouse click or hitting Enter) adds it to the tag input field, but does not submit it yet. You can continue adding more tags.
- The list of suggestions will disappear automatically when focus leaves the tags input field (e.g. when you click anywhere on the page) or when the new tags are submitted (by clicking on the "Tag" button or by pressing Enter in the input field when no tag suggestion is highlighted, as normal).
It's pretty bare-bones, but seems to work well.
Code:
autocomplete_tags_e_hentai_org.user.js.txt ( 7.86k )
Number of downloads: 133What it looks like:

The look and placement of the tag suggestion list is hardcoded, so if you want to change how it looks, you'll have to edit the block of CSS around line 54 in the script.