Looking at several CV writing blogs and tutorials, everyone suggests to call out your contributions something like this:
Developed project X with 50$ million profit.
Developed this application saving support team 100s of hours.
Is there a way for a developer who had been mostly fixing bugs for years at a company, with some bug fixing saving the company a vast amount of money, to call that out in their CV?
"Maintenance and support of project x, including major refactoring yy modules to allow integration with zz. This allowed the company to progress with MI reporting solution / comprehensive unit test framework / some other usefulness, resulting in a reduced total cost of ownership, a saving of approx $4m."
Repeat per project.
Mostly fixing bugs
Spin and emphasize (without lying) all the stuff that is not bugs in the same way.
Did you show anyone else how to fix it? That's team leading / mentoring (but don't lie).
Don't think of what you've been doing as defect resolution; think of it in terms of business benefit.
Aside - fix any spelling mistakes ("there", "their"). They will leap out far more at anyone reading your CV than bigging yourself up in the text. Your CV is a sales brochure and needs to be polished.
UPDATE
A number of commenters have pointed out that a developer would likely not know the $ value of their contribution, or maybe even the project as a whole. @puck points out that it may be detrimental, as an employer may not want their costs made public.
These are all valid points, and I generally agree, but note that as $ was mentioned in the original post, I included it in my example. For anyone uncomfortable with putting financial figures, try using another performance metric, e.g. (from my own CV):
Reduced database transactions from 4bn/week to 2.8bn/week leading to a direct reduction in hosting fees.
[I know exactly what that represented as a cost saving, as the CEO of that client was publicly ecstatic].
Is there a way a developer who had been mostly fixing bugs for years at a company with some bugs fixing saving company a vast amount of money call that out in their CV?
Yes - by simply calling that out as directly as possible!
I can assure you that someone who has spent years maintaining business critical software, keeping things running, saving the company a vast amount of money is exactly the type of engineer most companies would fall all over themselves to hire.
Bug-fixing is very skillful, crucial, high-impact work, and it's hard to find people who not only can do it well, but are happy and engaged doing it.
You don't say what your goals are, but if you are looking for similar types of work in future then I would go all-in on pitching yourself as an effective, proven bug-fixer and maintainer. Most teams need an engineer like this, and you're in a very niche talent pool because not many people pitch themselves like that.
To build on @Justin's answer, not only should you say what you did, you should spend a few words describing the project (what it does, what technologies it uses, how it is architected, etc.), so you have a chance to show off some of the stuff you are familiar with.
For example:
"Maintenance and support of project X, a > 1 million line distributed Java application, using Hazelcast, Kafka, and MongoDB, to collect realtime web usage data..."
Tracking down and correctly fixing bugs is quite often not trivial. Writing new code quite often is.
In addition to probably being able to debug code, you will have a better than average 'gut feeling' when confronted with a new bug - and you can read, understand and correct others' code. Any reasonable employer would recognize these skills as valuable on any team.
Assuming you now embrace your bug-finding skills, the question is whether you will be satisfied with being the bug-fixer or also want to participate on greenfield projects.
Be all about the specifics. What TYPES of bugs? I'm sure they weren't all typos.
Did you develop a procedure for checking/fixing? Or refine an existing one?
How many people or teams' bugs were you looking at? Were they in a variety of languages or other things showing that you can understand and switch between multiple things? Maybe sometimes it was a functionality fix, sometimes it was about improving security?
Use strong verbs : https://insights.dice.com/power-verbs-for-your-resume-and-cover-letter/ has some good ones under both the Technical and User/Technical Support sections.
From https://theinterviewguys.com/action-verbs-to-enhance-your-resume/ has these near "debugged"
Clarified, integrated, modified, overhauled, redesigned, restructured, transformed, adapted, debugged, regulated, restored, fabricated, remodeled
and some by "solved":
Capitalized, enhanced, expedited, stimulated, maximized , solved, strengthened, settled, reconciled, eased, elevated, negotiated, standardized, influenced, arbitrated, boosted
I also tend to like SquawkFox, here's their verb list: http://www.squawkfox.com/wp-content/uploads/2009/03/resume_action_words.pdf
One thing I notice on all of these: "Debugged" is a good, specific word! Hiring people probably are quite happy to see that this IS your skill/experience. Don't feel it's "lesser" than other programming. It's a cool skill-set, and those who need it will appreciate the thought you've given to explaining it well.
A line should be drawn between "developed" and "took part in development"; the first implies that the person either did it alone or had a major role in the project. CVs should aim to be truthful and detailed, and while it's the recruiter/interviewer's responsibility to verify the information, an untruthful CV would end up wasting both sides' time.
