Spot on about the setup hurdle being the real blocker. It's easy to overthink this.
But for a small team, that "another vendor account" point isn't always a negative. The checkbox approach locks you into GitLab's pace for updates and rules. A separate tool lets you control versions and roll back if a new rule breaks your build, which is a lifesaver when you're rushing a fix.
For your stack, Semgrep's community rules for Flask are seriously good out of the gate. You might get that checkbox simplicity and still have an escape hatch.
Happy customers, happy life.
That's a really solid point about version control being your escape hatch. It's something we actually rely on.
But that control comes with a real cost in alert fatigue during updates. When you pin a version, you miss new rules. When you update, you're the one sifting through a batch of new findings, some of which might be low-priority for your app. That's the hidden tax for avoiding GitLab's update pace.
For a small team, the question becomes: are you better at triaging code security findings or at managing vendor update schedules?
✌️
You're right about the monorepo advantage being significant for path exclusions. That brittle CI configuration becomes a genuine maintenance headache, especially when teams move code between internal packages.
I'd add a caveat about the rule exclusion system, though. While keeping it in the `.semgrep.yml` centralizes the logic, it also creates a single point of failure for scanning scope. An overly broad pattern exclusion written for one project can inadvertently skip scanning critical code in another if the config isn't namespaced carefully. The governance for these exclusions needs to be as rigorous as for the rules themselves.
It shifts the problem from managing job definitions to managing the precision of those exclusion patterns.
Migrate slow, validate fast.
The setup hurdle mentioned by user638 is real, but you can sidestep most of it for Semgrep. Don't overcomplicate the vendor thing right away.
Use their community rules with a simple Docker step in your CI, no account needed. That's about as complex as checking the GitLab box. You'll get a good feel for the quality on your code and see the false positive rate yourself before any commitment.
For Flask and React, I found the community rules caught the obvious stuff in both languages pretty well. The noise started when we got fancy with JSX props, but that seems universal.
Self-host or die trying.
> catching security issues before deployment without slowing down the devs too much
This is where you'll fail if you don't plan for triage. Both tools will spam you with findings right out of the gate, especially on dynamic frontend code. The difference is *where* you'll do the sifting.
If you want devs to own the noise, go with the config file approach (Semgrep). They'll groan at the extra PR step, but they'll learn the patterns that trigger false positives. If you want a central team or lead to gatekeep the noise, GitLab's UI lets you suppress things globally before the devs ever see them.
Pick the tool whose false positive workflow matches your team's tolerance for process friction. For a small team, I've seen the config file approach work better because the pain is distributed and visible. The UI approach hides the tuning until it becomes a bottleneck.
Totally agree about trying it locally first, it's a great way to get a feel. I run `semgrep --config auto` on new projects all the time.
Your point about the UI being a momentum killer is so real. It's friction right when you need speed. But just a heads up - that distributed control in the config file means every dev needs to be disciplined about using the suppression comments, or the noise just moves downstream.
That monorepo point is exactly why we switched. Path exclusions in a GitLab job YAML kept breaking after every other refactor.
But that rule exclusion system needs guardrails. We had a junior dev write a pattern like `exclude: tests/**` which was fine for his project. Then it got merged into the shared config and silently killed scanning for all Python unit tests across the board. Took a week to notice.
You get decentralization, but you also decentralize the blast radius of a mistake.
Benchmarks don't lie.
Oh, the false positive point is huge. We tried setting up a basic scan and got buried in alerts for React prop types that were intentional. It really does come down to who's going to filter that noise. For a small team, I'd lean towards Semgrep's config file like others said, so everyone learns what to ignore. Has anyone actually found the GitLab UI suppression less annoying in practice?
Still learning
Exactly the trap we fell into. The GitLab UI suppression felt less annoying for about two months. It was a clean, centralized audit trail. But it created a "security team" bottleneck by accident.
Every new alert required a ticket or a Slack ping to the one person with permissions to suppress in the UI. Devs couldn't just add a `# nosemgrep` comment and move on. That central control killed the dev-ownership model and became the single point of failure.
So it's less annoying per alert, but it creates a process monster. For a small team, that's often worse than the initial noise.
Implementation is 80% process, 20% tool.
Yeah, that "six months tuning" phase is exactly what kills momentum. I've seen teams get so bogged down in committee reviews for each suppression that the tool just becomes shelfware.
One nuance to your point: while killing a rule in `.semgrep.yml` is fast, you need a light process to make sure you're not disabling something important because it was a hassle that one time. We use a simple rule: any rule exclusion needs a one-line comment linking to a PR or issue explaining why. It keeps the config self-documenting and stops the "just delete it" reflex from creating blind spots later.
That small bit of discipline lets you keep the velocity without the technical debt.
Sleep is for the weak
Great question, and perfect timing - my team just went through this exact comparison for a similar stack.
For your main goal of not slowing down devs, I'd say start with Semgrep's community rules in a local test. The false positives for Flask were surprisingly manageable, but React JSX gave us a handful of weird ones, like flagging certain prop destructuring patterns. The key was adding `# nosemgrep` comments directly in the code - it felt lightweight and the devs learned to recognize the patterns quickly.
One thing I haven't seen mentioned yet is the learning curve. The Semgrep config feels more like writing code, which our devs picked up faster than navigating GitLab's UI suppression workflows. That made a real difference in adoption speed for our small team.