Getting 503? Here’s why it happens and the exact fix.
You are seeing 503 because the target server is temporarily unable to handle requests. The fix: wait and retry with backoff, or switch to a different proxy exit if the target is region-specific.
Visit the target URL in a browser. If it returns 503 there too, the server is genuinely unavailable.
If the browser works but your proxy does not, the 503 is a bot block in disguise. Switch to residential with browser headers.
Check the response for a Retry-After header. Wait at least that long before retrying.
Your request volume may be contributing to the overload. Throttle to 5-10 requests per second per domain.
import requests
import time
proxy_resi = "http://USER:PASS@gw.knoxproxy.com:7000"
headers = {
"User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) "
"AppleWebKit/537.36 Chrome/125.0.0.0 Safari/537.36",
"Accept-Language": "en-US,en;q=0.9",
}
def smart_fetch(url, max_retries=3):
for attempt in range(max_retries):
r = requests.get(url, proxies={"https": proxy_resi},
headers=headers, timeout=30)
if r.status_code == 503:
retry_after = int(r.headers.get("Retry-After", 5))
print(f"503 -- waiting {retry_after}s (attempt {attempt+1})")
time.sleep(retry_after)
continue
return r
return r # return last response for logging
r = smart_fetch("https://target.example/api")Test your setup with our proxy checker, then contact support if 503 still won’t clear.
A 503 Service Unavailable means the target server exists but cannot handle your request right now. Unlike 502, the server explicitly signals it is overloaded or in maintenance. Some anti-bot systems also return 503 as a soft block -- telling bots to go away without revealing the real block reason.
Reduce your request rate to the target. Implement exponential backoff. Wait for the Retry-After header if present.
Switch to residential proxies with browser-like headers. The target is detecting proxy traffic and returning 503 instead of a proper block page.
This is temporary. Retry in 5-15 minutes. CDN maintenance windows are typically short.
If 503 persists with residential proxies and browser headers, the target may be running JavaScript-based bot detection. Contact KnoxProxy support to discuss browser fingerprint solutions.
If it is genuine server overload, it is temporary -- typically minutes to a few hours until the target recovers. But if it is an anti-bot block disguised as a 503 response, it will persist indefinitely until you switch to residential proxies and add browser-like headers to your requests.
Load the same target URL in a plain web browser without any proxy attached. If the browser gets a 200 response but your proxy request gets 503, the target is using 503 as a disguised bot-detection response rather than a genuine overload signal.
No. KnoxProxy bills only successful responses, so 503 errors never count against your bandwidth allowance. They are free and, depending on your configuration, can be automatically retried through a fresh proxy IP without any manual intervention or extra charge on your account.
KnoxProxy comes pre-configured to avoid the most common errors. Get started and fix 503 for good.