proxy-test - SKILL.md Agent Skill

name: proxy-test description: Verify ublproxy ad-blocking behavior by comparing responses with and without the proxy using curl. Use when the user asks to test, verify, or compare proxy behavior against a website. allowed-tools: Bash(curl:), Bash(mise:), Bash(diff:*)

Verifying Proxy Behavior with curl

Test ublproxy's ad-blocking (request blocking and element hiding CSS injection) by comparing curl responses with and without the proxy.

Prerequisites

The proxy must be running with a blocklist:

# Start the proxy with adblock rules
mise run dev -- --blocklist examples/is.rules

Verification workflow

1. Find rules for the target domain

Before testing, check what rules the blocklist has for the target domain:

# Element hiding rules (##)
grep "example.is##" examples/is.rules

# URL blocking rules (||)
grep "||.*example" examples/is.rules

# Global element hiding rules (apply to all domains)
grep "^##" examples/is.rules

2. Verify request blocking

Blocked hostnames return 403 for HTTPS (CONNECT) requests:

curl -v --proxy https://127.0.0.1:8443 --proxy-insecure -k https://blocked-domain.com 2>&1 | grep "< HTTP"
# Expected: HTTP/1.1 403 Forbidden

3. Verify element hiding CSS injection

Element hiding injects display: none !important CSS rules into HTML responses. Check for the injected style tag:

curl -s --proxy https://127.0.0.1:8443 --proxy-insecure -k https://example.is | grep 'display: none'

4. Compare proxy vs direct

Save responses and diff them to see exactly what the proxy changed:

curl -s --proxy https://127.0.0.1:8443 --proxy-insecure -k https://example.is > tmp/with-proxy.html
curl -s https://example.is --compressed > tmp/without-proxy.html
diff tmp/without-proxy.html tmp/with-proxy.html

Example: testing against an Icelandic site

# Terminal 1: start proxy
mise run dev -- --blocklist examples/is.rules

# Terminal 2: check what rules apply
grep "1819.is" examples/is.rules

# Compare responses
curl -s --proxy https://127.0.0.1:8443 --proxy-insecure -k https://1819.is > tmp/with-proxy.html
curl -s https://1819.is --compressed > tmp/without-proxy.html

# Check for element hiding CSS injection
grep 'display: none' tmp/with-proxy.html

# Diff to see all changes
diff tmp/without-proxy.html tmp/with-proxy.html

Troubleshooting

"proxy is not running" — start the proxy first with mise run dev -- --blocklist examples/is.rules
Connection refused — verify the proxy is listening: curl --proxy https://127.0.0.1:8443 --proxy-insecure -k https://example.com
No CSS injection — the page may not be HTML, or the response may use zstd compression (not yet supported). Check Content-Encoding with curl -D-.
Elements not found — the site may have been redesigned since the blocklist rules were written. The selectors may no longer match anything in the server-rendered HTML (some elements are only added by JavaScript at runtime).