To find out whether a proxy is working, compare the same request with the proxy off and on in the exact app you care about, then check DNS, WebRTC, IPv4 and IPv6 separately. A successful request only confirms that one traffic path worked; it does not show that every app or protocol uses the proxy.
1. Define what the proxy is supposed to route
Before testing, write down the routing expectation. Is the proxy configured for one browser, one application, or all system traffic? Should DNS queries go through it or resolve locally? Should IPv6 be proxied, blocked, or allowed directly? What should the browser do with WebRTC traffic?
A result counts as a leak only when it contradicts that intended boundary. For example, local DNS resolution is not a failure if your setup is meant to resolve names locally. This distinction helps avoid treating every difference as a security problem. Mexela’s proxy leak testing guide recommends testing these behaviors separately.
- Client or app being tested
- Protocols expected to use the proxy
- Expected DNS behavior
- Expected IPv4 and IPv6 behavior
- Expected WebRTC behavior
2. Capture a direct baseline
With the proxy disabled in the test client, make a request to a neutral HTTPS endpoint you control or explicitly trust. Record the public address it reports and whether the address is IPv4 or IPv6. Note DNS and WebRTC observations as private comparison data; avoid including sensitive network details in a report shared publicly.
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Use the same endpoint and client for the proxied test. Keeping conditions consistent makes it easier to attribute a change to the proxy rather than a different site, app, or network.
3. Verify the HTTP or HTTPS exit in the exact client
Enable the proxy in the browser or application whose traffic matters, then repeat the same neutral request. Check that the observed exit matches the assigned proxy or its documented pool behavior, and confirm that TLS certificate validation succeeds. Also check that a bypass rule did not exclude the test host.
A changed IP is useful evidence, but an expected exit is stronger: an unrelated changed address does not establish that the configured proxy handled the request. If the baseline address still appears, check whether the app accepted the proxy settings, whether the proxy supports the request’s protocol, and whether a bypass rule matched.
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For a one-request command-line check, curl supports the --proxy (or -x) option. Its manual documents HTTP proxy selection and SOCKS schemes including socks4://, socks4a://, socks5:// and socks5h://. Replace the placeholders below locally and use an endpoint you control or trust:
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curl --proxy http://PROXY_HOST:PORT https://YOUR_TRUSTED_IP_CHECK_ENDPOINT
This checks only that curl request path, not the browser, DNS, WebRTC, or other apps. Keep TLS verification enabled: if the request succeeds only after verification is disabled, treat that as a certificate or trust problem, not a successful test. The official curl manual advises obtaining sensitive credentials from a file or similar source instead of putting them in clear text on the command line, where other users on the system may briefly see them. Do not put real credentials in an article, screenshot, shell history, or shared report.
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4. Check DNS behavior independently
Compare observed resolver and query behavior with the routing expectation you wrote down. Some client modes resolve host names locally; others can arrange resolution through the proxy. A browser’s secure-DNS setting may also differ from the operating system’s resolver settings.
A resolver appearing to be in the proxy’s country does not prove that the proxy performed the lookup. If the HTTP exit is correct but DNS appears different, first determine whether local resolution is allowed, then check the proxy client’s resolution mode and the browser’s secure-DNS behavior.
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5. Inspect WebRTC separately
WebRTC uses ICE to find possible connectivity paths, including mechanisms involving STUN and TURN. Those media paths are distinct from ordinary page HTTP requests, so do not assume a conventional browser proxy setting carries WebRTC traffic. The W3C WebRTC specification and MDN’s overview of WebRTC protocols describe this separate connectivity behavior.
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Test the browser policy you intend to use with a controlled call or diagnostic. Interpret the candidate type as well as the address: private or obfuscated host candidates are not equivalent to a public address that contradicts your routing expectation. A different candidate warrants investigation, but its meaning depends on the candidate and your intended policy.
6. Test IPv4 and IPv6 as separate routes
If your connection supports both address families, test each one and compare the observed route with the design. An expected IPv4 proxy exit does not establish that IPv6 traffic is captured. If IPv4 looks right but IPv6 does not, confirm whether IPv6 is meant to use the proxy and test that family directly.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.7. Test the real destination after the neutral checks
Once you understand the basic route, make one safe request to the intended service. A failure there may reflect destination policy or compatibility rather than basic proxy reachability. Avoid starting with an account-heavy site: cookies, redirects, scripts, and policy responses can obscure which path is failing.
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How to interpret common results
| Observation | What it establishes or suggests | Next check |
|---|---|---|
| Expected exit and valid TLS | This request completed through the configured route; it says nothing about other clients or protocols. | Continue with DNS, WebRTC, IPv4, and IPv6 checks if they are in scope. |
| Baseline address still appears | The tested app may not have accepted the setting, the proxy may not support that protocol, or a bypass rule may have matched. | Verify app-level settings, supported protocol, and bypass rules. |
| HTTP exit is expected but DNS differs | DNS may be resolving locally, depending on the client and browser settings. | Check whether local resolution is allowed, the client’s resolution mode, and browser secure DNS. |
| WebRTC reports another candidate | WebRTC has connectivity paths separate from the ordinary HTTP request; candidate type and policy determine whether the result conflicts with expectations. | Review the candidate type and test the intended browser policy. |
| IPv4 looks right but IPv6 does not | The IPv4 result does not establish IPv6 routing. | Confirm the intended IPv6 behavior and test that family directly. |
| curl works but the app or browser does not | Settings may be client-specific, limited in scope, or affected by bypass behavior. | Use the exact client, change one setting at a time, and repeat the same comparison. |
| TLS fails unless verification is disabled | This indicates a certificate or trust issue, not a verified successful proxy request. | Keep certificate verification on and investigate the trust problem. |
What a proxy test cannot prove
A diagnostic speaks only to the paths and conditions it tested. One successful HTTP request does not establish that every application, DNS lookup, WebRTC connection, or address family uses the same route, and a proxy is not a general anonymity guarantee.
Unknown free proxies also deserve caution. A 2024 study by Naif Mehanna, Walter Rudametkin, Pierre Laperdrix, and Antoine Vastel collected 640,693 proxies from 11 providers over 30 months; 34.5% were active at least once during the study, researchers identified 4,452 vulnerabilities in services on proxy IP addresses, and 16,923 proxies altered content at least once. These findings apply to the study’s collected public free-proxy population and methodology, not to all providers or paid services; they do not establish that any particular paid service is safe. Read the study, “Free Proxies Unmasked: A Vulnerability and Longitudinal Analysis of Free Proxy Services.”
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