Summary
This article explains why Dynatrace Browser monitors may fail to block specific requests and how to resolve it.
The issue is caused by a limitation in the Chrome Extension platform (MV3), which restricts the length of regular expressions used in request-blocking rules
Problem
When configuring Block specific requests in a Dynatrace Browser monitor:
- Requests aren't blocked as expected
- Configuration can't be saved
- Validation or changes fail silently
Error Behavior
You may observe:
- Blocking rules not applied
- Unable to save monitor configuration changes
- Only partial edits allowed (e.g., name or frequency updates)
Cause
The Dynatrace Synthetic Recorder (a Chrome extension) is subject to Manifest V3 (MV3) limitations.
As a result:
- Regular expressions used in Block specific requests
- Cannot exceed 90 characters
If the limit is exceeded:
- The rule is ignored
- Configuration changes can't be saved fully
Resolution
✅ Fix – Reduce the regex or match pattern length
Ensure your blocking rule:
- Is ≤ 90 characters
- Uses simplified or more efficient matching
✅ Example
❌ Too long (will fail)
https://example.com/api/very-long-path-with-multiple-query-parameters-and-dynamic-values
✅ Shortened pattern
example.com/api/*
✅ What to expect after fixing
Once the pattern is shortened:
- Blocking rules are applied correctly
- Full configuration becomes editable again
- Save operation succeeds
Important Notes
- This is a platform limitation, not a Dynatrace bug
- Applies specifically to:
- Browser monitors
- Request-blocking rules using regex or match patterns
Limitations
If the rule exceeds the length:
- 🚫 Blocking does not work
- 🚫 Some monitor settings cannot be saved
- ✅ Only basic properties (name, thresholds, frequency) can still be modified
Best Practices
- ✅ Use short, wildcard-based patterns instead of long regex
- ✅ Avoid including full URLs with query strings
- ✅ Break complex rules into simpler patterns where possible
- ✅ Validate pattern length before saving
When to Use This Guide
Use this troubleshooting when:
- Blocking requests doesn't work
- Monitor configuration fails to save
- You are using long regex or URL match strings
What’s Next
If the issue persists
- Review all request-blocking patterns
- Confirm each is within the 90-character limit
-
Open a chat and provide
- a link to the browser monitor that you're troubleshooting.
- an explanation of the behavior you're seeing, and what you're expecting.
- the troubleshooting steps you have already completed.
Related reading
📖 Configure browser monitors
📖 Synthetic Troubleshooting Map
