Set minimums for header values like Pack Size and Item Rarity, pick the waystone modifiers you are after, and this page builds the search string. Paste it into the stash search to highlight the waystones worth running.
Quoted groups separated by spaces, all of which a waystone has to match: rarity first, then the header values, then the modifiers you selected. Your custom text goes last, added without quotes exactly as you type it. Anything you leave unset adds nothing, and ticking every rarity is the same as ticking none.
How do the header value minimums work?
Item Rarity, Pack Size, Monster Rarity, Monster Effectiveness and Waystone Drop Chance each take a minimum from 1 to 999 percent; leave a field empty to ignore it. Pack Size of at least 15 becomes ze: \+(1[5-9]|[2-9].|\d..)%, which only fits the header line, never a modifier line or a negative value.
Are header values and modifiers matched separately?
Yes. The header values have their own any/all switch: any accepts a waystone that reaches at least one of your minimums, all needs every one. The switch under Modifiers to include does the same for the modifiers, independently.
Can I search for something the filters do not cover?
Use Custom text. It is added to the end exactly as you type it, without quotes or escaping, so you can write your own group, a negation with ! for example.
What if the string gets longer than 250 characters?
The builder assumes the in-game search field takes 250 characters. The counter turns red past that, but the string is never shortened for you. Every all-mode group costs extra quotes and a space, so switching a long list to any is the quickest way back under 250 characters.