Browser monitors: Unable to block specific requests (owing to limitations on the length of regular expressions)

nandini_balakri — Fri, 12 Jun 2026 08:42:49 GMT

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.

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