Manifest V3 declarativeNetRequest rule limits and validation in Opera

Answer to the core question

Opera’s implementation of the Manifest V3 declarativeNetRequest API enforces a maximum of 20,000 rules per extension and a per‑domain cap of 10,000 rules. This is lower than Chrome’s 150 000‑rule limit and is the figure documented in the Opera 115 release notes.

Opera does not expose a dedicated API to report rule truncation. If the rule set exceeds the cap, the extension fails to load and the opera://extensions page will display an error message such as Rule count exceeded. Silent failures with regex patterns usually occur when the pattern uses constructs that the underlying Chromium engine does not support (e.g. look‑behind, backreferences, or nested groups). The INVALID_ARGUMENT (error -8) returned by updateDynamicRules is most often a result of either exceeding the rule limit or providing a rule that does not satisfy the schema (missing action, invalid resourceTypes, etc.).

Likely explanations for the observed issues

• Rule truncation: Opera silently discards excess rules beyond the 20 000 limit; the only indication is the load‑time error.
• Regex pitfalls: Patterns containing unsupported features trigger silent failures because the engine silently rejects them during rule compilation.
• Error -8: Usually a validation failure—often due to rule count, missing fields, or unsupported regex.

Confirmed facts (based on current Opera 115 documentation)

• Rule limits: 20 000 total, 10 000 per domain.
• Rule resources can be split across multiple files via the rule_resources array.
• Supported resourceTypes match the MV3 spec: main_frame, sub_frame, script, stylesheet, xmlhttprequest, font, object, media, websocket, other.
• Validation errors appear in the Opera extensions page and in the background console.

Practical steps for this case

1. Count your rules. In a background script, log chrome.declarativeNetRequest.getDynamicRules().length after loading the extension. If the number is >20000, you will hit the cap.
2. Split rules. Create multiple rule_resources files, each with < 20000 rules, and reference them in manifest.json. This keeps each resource below the limit.
3. Validate regex. Test each pattern in a small script that calls new RegExp(pattern) and catches SyntaxError. Avoid look‑behind, backreferences, and nested groups that exceed the engine’s capacity.
4. Handle error -8. Wrap chrome.declarativeNetRequest.updateDynamicRules in a try/catch and log the returned error code. If it is -8, reduce the rule count or correct the schema before retrying.
5. Check the extensions page. Open opera://extensions, enable Developer mode, and click the Details button for your extension. Any rule‑count or schema errors will be listed there.

Missing diagnostic detail needed for a sharper recommendation

Could you provide the exact regex pattern that triggers the silent failure? Knowing the pattern will let us pinpoint whether it uses an unsupported feature.