Partwise
Your shop's search finds SKUs, size SKUs, GTINs and part numbers - however the customer types them.
Partwise is for parts, hardware and spares shops, where customers search by the number on the old part.
Inside Partwise
Every number
SKU, each size's SKU (finding the product it belongs to), GTIN/UPC/EAN, a maker's part number from any product field you name, and an "Other part numbers" field for the numbers a part replaces or is cross-referenced to.
However it is typed
dashes, spaces, dots and capitals do not matter - "omc 0398 752" finds OMC-0398752.
Look-alike characters forgiven
O and 0, I and L and 1, S and 5, B and 8, Z and 2 - read off a worn label.
Part of a number
"0398752" finds OMC-0398752 (you choose how many characters first).
In the right order
exact, then look-alike, then starts with, then contains - above the ordinary word matches.
Straight to the product when exactly one product has the number.
"The nearest:" when nothing matches, the closest part numbers, two characters off at most - for swapped digits.
Says what matched under each search result.
Before you start
Asked first
Does it slow the search down?
It keeps its own small index of the numbers, looked up by key - it does not read every product on every search.
Does it replace my search box?
No. It widens the shop's own search, so your theme's search box and results page stay as they are.
More for the storefront
Addendum
Extra product fields with prices, and a customer artwork upload - checked by what the file really is, kept private.
Admittance
Sell event tickets as WooCommerce products, email a named ticket with a QR code per seat, and check people in at the door from a phone.
Chit
One store-credit balance per customer - no codes. Refund as credit, give credit with a reason, spend it at checkout.