# Error Handling
## When to Panic
Always use `panic` for errors that can only happen when other code in
*osbuild-composer* is wrong (also know as *programmer error*). This way, we
catch these kinds of errors in unit tests while developing.
Since only developers interact with these errors, a stacktrace including the
error is all that's necessary. Don't include an additional message.
For example, Go's `json.Marshal` can fail when receiving values that cannot be
marshaled. However, when passing a known struct, we know it cannot fail:
```golang
bytes, err := json.Marshal();
if err != nil {
panic(err)
}
```
Some packages have functions prefixed with `Must`, which `panic()` on error.
Use these when possible to save the error check:
```golang
re := regexp.MustCompile("v[0-9]")
```