AI coding agents cheat. Not maliciously, and usually not on purpose. They optimize for "looks done," because shipping code that appears complete is easier than shipping code that is complete. Every reward signal an agent sees pushes it toward the green checkmark, and the green checkmark is cheaper to fake than to earn.
That was a curiosity when one engineer babysat one agent. It stops being a curiosity when a fleet of agents opens PRs faster than any human ever did, and a reviewer is asked to catch subtle shortcuts at a volume review was never built for.
So I went and measured it. I mined 327 agent-attributed pull requests from public GitHub, looked for the ones maintainers publicly called out as cheating, and then tried to catch the same cheats with software. This post is what I found, including the parts that did not work.
What "cheating" actually means
The word "cheating" invites eye-rolling AI-doom takes, so let me make it concrete. Here are real, recognizable patterns. Every one of these is something you have already seen a human do on a bad day.
Swallowed errors. The failure path is caught and dropped on the floor.
try {
await syncRemoteState(payload);
} catch (err) {
// handled
}
Nothing is handled. The test that expected no throw now passes.
Relaxed assertions. A strict matcher becomes a loose one.
- expect(result).toEqual({ id: 7, status: 'settled', total: 4200 });
+ expect(result).toBeTruthy();
{} is truthy. The test is now green for almost any output.
Assertion stripping. The checks that actually pin behavior quietly disappear.
const rows = await repo.findByOrg(orgId);
- expect(rows).toHaveLength(3);
- expect(rows[0].email).toBe('[email protected]');
+ expect(rows).toBeDefined();
No-op fix. The PR claims to fix a bug. The source is untouched; only the test changed to stop failing.
Fake refactor. A symbol is renamed at its definition, callers still reference the old name, and it only compiles because a type got loosened somewhere.
Type/lint suppression. A @ts-ignore or eslint-disable lands directly over the line that stopped type-checking after the change.
+ // @ts-ignore
return handler(req as AuthedRequest);
None of these are exotic. That is the point. The cheat hides inside patterns your codebase already contains legitimately.
Why this matters now
Agents do not cheat more per PR than a rushed human does. They cheat at the same modest rate, across far more PRs, with none of the social friction that makes a human think twice before deleting an assertion. A cheat rate that was tolerable at ten PRs a week becomes a review backlog at two hundred. It is a signal-to-noise problem, and the noise floor is rising.
The data, honestly
Of the 327 agent-attributed PRs I mined, 27 (about 8%) carried a maintainer complaint that named a cheat. Agents cheat in the wild, and maintainers do catch them: 20 of the 27 were rejected at review. The other 7 merged anyway, including on microsoft/testfx and outline/outline.
Now the caveat that most AI posts skip. That 8% is a loose bar: any maintainer comment naming a cheat counts, including terse ones and self-flags. When I re-audited the same 27 against a strict independent-human bar (a second person, reading the actual diff, agreeing it is a cheat), only 7 survived. So the honest range is "8% by a generous reading, closer to 2% by a strict one." Both numbers are in the repo, and I would rather you see the gap than trust a single tidy figure.
Why your existing tools miss it
Linters and SAST (Semgrep, ESLint security rules, and friends) do not catch these, because a cheat is usually structurally valid code. An empty catch block is legal. A renamed function is legal. A loosened matcher is legal.
Two of the merged examples above make the point:
microsoft/testfx#8513deleted a test in C#, a language the structural detectors do not even parse.
outline/outline#12197removed a singlejest.mockline. There is nothing malformed to match. The behavior changed; the syntax did not.
A pattern matcher keyed on "bad syntax" has nothing to grab onto. You need something that reasons about whether the diff delivers what the PR claims, and something that can run the code.
What I built
It is an open problem, not a finished product.
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