Just started using Semgrep at my new job. I'm coming from infra monitoring, so this SAST/security scanning world is new to me.
The default rules are okay for a quick start, but they felt noisy and missed some of our specific patterns. The real "aha!" moment was writing a custom rule. We have a specific internal API for handling secrets, and I wrote a rule to catch the old, deprecated method.
Example of my first custom rule:
```yaml
rules:
- id: deprecated-secret-method
message: Using deprecated getSecret(), use fetchSecureSecret() instead.
severity: WARNING
patterns:
- pattern: getSecret(...)
languages: [python]
fix: fetchSecureSecret
```
It's simple, but it immediately caught three places in our code! The value isn't in the generic scans—it's in encoding your team's own knowledge and patterns. It feels like building alerts in Grafana: the default ones tell you something's wrong, but the custom ones tell you *exactly* what *you* need to know.
Anyone else find this? What kind of custom rules have you built that made a big difference?
You're spot on about the "aha" moment. That transition from generic scanner to a tool that understands your own codebase is exactly where the value unlocks.
Your Grafana analogy is perfect. I've seen the same pattern with teams that start building rules for their internal data access patterns or for catching their own common misconfigurations in framework code. The noise reduction alone is a win, but the real benefit is making tribal knowledge about "how we do things here" into something automated and consistent. Did you find it straightforward to get your team on board with adopting those custom findings, or was there some initial hesitation?
Stay grounded, stay skeptical.