Find where your discount codes are listed

In short

A code given to one audience rarely stays there. Voucher sites list codes their members, staff and partners find, and coupon extensions offer them at checkout.
Google Search finds pages that mention a code: put it in quotes, use site: for one domain and before: or after: by date. Google says results aren't always complete.
Coupon extensions don't show up in a search. Their codes appear inside a checkout, so you read their listings, or a tool that does, instead.
A listed code usually costs a discount plus commission on a shopper who was already at your checkout, credited to whoever had the last click.
Most listings have an ordinary route: a public code, a partner's code listed as agreed, or a shopper passing one on. Ask before deciding anything.

Yourbrand sends new newsletter subscribers a 15% welcome code. A fortnight later, its affiliate manager notices that code on orders credited to a voucher site publisher, a few a day, then a few dozen. Nobody gave the code to a voucher site. So where is it listed, how did it get there, and what is it costing?

What the trade calls code leakage is mostly codes doing what codes do: being passed on. This guide covers the routes a code takes, how to find each listing with Google's own tools, what the coupon extensions see that a search doesn't, and how to work out whether a listing matters.

How codes travel

Voucher sites list codes for thousands of stores. Codes reach them from their own members, from their staff, from brands and networks that send them, and from other sites. Many are publishers on affiliate programmes, earning commission on the sales they refer.
Coupon extensions are browser add-ons that offer codes when a shopper reaches a checkout. Some providers say a code was caught at checkout: seen being used there.
Search ads on searches such as “yourbrand discount code”, from sites with a page of your codes behind them.
Shoppers and creators: forums, group chats and social posts, where a code shared with one person reaches many.

Google's Chrome Web Store has a policy for extensions that earn from affiliate links. Its Affiliate Ads page, last updated on 11 March 2025, says an extension must disclose any affiliate programme, may only add affiliate links, codes or cookies when the user gets a direct benefit such as a discount or cashback, and needs a related user action before each one. So when a shopper accepts an extension's offer, the extension can add its own affiliate link at that moment, and a sale through it can be credited to the extension.

What a listing costs

Imagine: one order with a listed welcome code

Basket: £60.00
The code's 15% off: £9.00
Commission at 5% of the £51 paid: £2.55
Network fee at 30% of commission: £0.77
Cost of an order that was already at your checkout: £12.32

Most programmes credit the sale to the publisher with the last click before the order, within the cookie window. A shopper who leaves your checkout to look for a code, and comes back through a voucher site, ends with that site's click. That's how a code meant for new subscribers can end up paying a discount and a commission on the same order. Whether it should is a matter for your terms and the code's own terms, and your network can hold the commission while you look, within your validation window.

Finding listings with Google Search

Google documents a handful of search operators in its Refine Google searches help page. They're the quickest way to find pages that mention a particular code.

Quotes search for an exact word or phrase: "YBNEWS15" finds pages with that code on them.
Minus leaves a word or site out: "YBNEWS15" -site:yourbrand.example drops your own pages.
site: keeps results to one domain, with no space after the colon: site:dealpages.example yourbrand. It includes subdomains.
before: and after: filter by when a page was last updated: "YBNEWS15" after:2026-10-01.

Google's Search Central documentation says the list of URLs a site: search returns is not always exhaustive, and that operators are bound by indexing limits. A page that isn't indexed, is behind a login or was updated since Google last read it won't show. Google's cache: operator, once a way to see an older copy, stopped working in September 2024.

Google's Advanced Search page does the same through fields: all of these words, this exact word or phrase, none of these words, site or domain, and Last update, with Any time, Past hour, Past 24 hours, Past week, Past month and Past year. For a new code, Past week is a useful first look.

Watching for new listings with Google Alerts

Google Alerts emails you when new pages match a search. Enter the code, or your name with “discount code”, then Show options: How often (As-it-happens, At most once a day or At most once a week), Sources (Automatic, News, Blogs, Web, Video, Books, Discussions or Finance), Language, Region and How many (Only the best results or All results). Then Create Alert. An alert for each code you'd least like to see listed is a cheap early warning, with the same limits as Search: it only knows pages Google has indexed.

Reading a listing

The code and what it gives. Is it yours, current, and the offer it claims?
Where the provider says it came from. Some list a source: shared by a member, caught at checkout, from an affiliate, or found elsewhere.
The provider's own figures, such as a success rate or when it last worked. They're the provider's claims, not a test.
The link to your shop. Copy it without clicking. It usually carries a network's domain and the publisher's id, which tells you whose sale it would be.
When it appeared. A listing that arrived the week after a newsletter went out has a likely route.

How to find your codes, step by step

List your live codes: who each was given to, what it gives, whether it's single-use, and when it expires.
Search each code in quotes on Google, leaving out your own site with -site:, and note every page that lists it.
Set the date to Past week or use after: to find listings that appeared since a code went out.
Create a Google Alert for each code that was never meant to be public.
Check the coupon extensions and voucher sites that matter to your programme, or a record that reads them for you.
For each listing, note the provider, the source it gives, the date and the link to your shop, copied without clicking.
Match the listings to your network's report of sales with each code, and to the publisher whose click they carried.
Decide code by code: leave it, end it, replace it with a single-use or partner-specific code, or raise it with your network.

If you work with creators, codes are also part of disclosure. The UK's Competition and Markets Authority says in its guidance for content creators that using a discount code or an affiliate link isn't enough on its own to show a post is an ad, so a creator's code is no substitute for a clear label.

The ordinary explanations

The code was public: a sitewide sale code in your own ads, emails or homepage banner.
It was given to a voucher or cashback partner, which listed it as agreed.
A subscriber, customer or member of staff passed it on, and a voucher site's members submitted it.
A creator's audience shared it further than the creator's own posts.
It follows a common pattern, such as a word and a number, and shoppers tried it.
It expired and the listing hasn't caught up, which costs nothing because it no longer works.

How affiliate marketing works covers the kinds of publisher, and How a sale gets credited the last click. The guide to reading an affiliate link takes a listing's link apart.

Sources

Google's own help and policy pages first, then the papers by their titles. Each was read on the date above; Google's pages change, so check the current wording before you quote it.