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 overload, it is temporary -- minutes to hours. If it is an anti-bot block disguised as 503, it will persist until you change your proxy type and request profile.
Load the same URL in a browser. If the browser gets 200 but your proxy gets 503, the target is using 503 as a bot-detection response.
No. KnoxProxy bills only successful responses. 503 errors are free and automatically retried through a fresh IP.
KnoxProxy comes pre-configured to avoid the most common errors. Start a free trial and fix 503 for good.