Proxomitron Alternatives: Modern Tools for Web Filtering

Proxomitron Tips: Advanced Filters and Performance Tweaks

Overview

Proxomitron is a local web-filtering proxy that modifies HTTP(S) traffic using user-defined filters. These tips focus on advanced filter techniques and performance tweaks to reduce bandwidth, speed up browsing, and improve privacy and compatibility.

1. Organize filters for maintainability

• Use categories: Group filters by purpose (ads, tracking, layout fixes, scripts).
• Name consistently: Prefix rules with short tags (e.g., “AD-”, “TRK-”, “CSS-”) to find and edit quickly.
• Comment liberally: Add brief comments explaining why a rule exists and when it can be removed.

2. Prefer targeted rules over broad ones

• Match specific hosts/paths: Use host and path constraints to avoid unintended side effects.
• Limit regex scope: Anchor patterns (e.g., ^ and $) and use non-greedy quantifiers to reduce CPU use.
• Avoid blanket replacements: Rewriting large chunks of HTML/CSS can break pages and slow processing.

3. Optimize regular expressions

• Use atomic grouping and non-capturing groups: Replace (…) with (?:…) when you don’t need captures.
• Avoid excessive backtracking: Replace patterns like .?foo with more precise character classes (e.g., [^<]?).
• Test with sample pages: Validate regex performance on representative pages before enabling globally.

4. Block efficiently: prioritize and combine

• Order rules by cost: Put inexpensive hostname/path checks before expensive regex or script parsing.
• Combine similar blocks: Merge multiple simple host-block rules into one rule with alternation when safe.
• Use quick rejects: For known ad domains, return a small 1×1 GIF instead of processing full responses.

5. Use content-type checks

• Filter by MIME type: Apply heavy HTML/CSS/JS transformations only when Content-Type matches text/html, text/css, or application/javascript to avoid wasting CPU on images or binary downloads.
• Skip large responses: Set size thresholds to bypass transformations on very large responses (e.g., >1 MB).

6. Cache and reuse results

• Enable caching: Use Proxomitron’s caching for static resources to reduce repeated processing.
• Cache filter outputs: Where possible, cache the result of expensive rewrites keyed by URL and headers to reuse across requests.

7. Tackle scripts safely

• Block or rewrite trackers early: Remove known tracker scripts by host before executing complex DOM rewrites.
• Prefer blocking over modification: If a script only tracks, blocking it reduces CPU compared to rewriting it.
• Use minimal script edits: When modifying JS, change only the necessary tokens or function calls to avoid introducing errors.

8. Optimize CSS and layout fixes

• Use concise selectors: Target elements by ID or class rather than long selector chains.
• Prefer hiding over removal: Using simple display:none rules is faster and safer than reconstructing HTML.
• Batch style injections: Inject a single

9. Monitor performance and errors

• Enable detailed logging temporarily: Track slow rules and exceptions, then revert to minimal logging.
• Measure per-rule latency: Identify hotspots and optimize or disable rules causing delays.
• Use test profiles: Create a performance profile with only essential filters to compare baseline speeds.

10. Maintain compatibility

• Whitelist critical domains: Bypass or relax filters for payment gateways, banking, or other sensitive services.
• Use site-specific exceptions: Create targeted exceptions rather than disabling entire categories.
• Keep backups: Save filter sets before large changes to revert quickly if pages break.

Example: Efficient ad-blocking filter (concept)

• Host match: ads.example.com OR doubleclick.net
• Content-Type: text/html, application/javascript
• Action: return 1×1 GIF for requests under 50 KB; otherwise block headers with 204 No Content.

Final checklist

• Group and comment rules
• Target matches precisely
• Optimize regexes and order rules by cost
• Use content-type and size checks
• Cache outputs where possible
• Monitor and profile performance
• Maintain targeted exceptions for compatibility

Following these guidelines will help you build robust Proxomitron filters that improve browsing speed, reduce resource use, and minimize page breakage.