Solve full-page Cloudflare interstitials ("Just a moment...", I'm Under Attack mode, invisible challenges) and receive a cf_clearance cookie bound to your proxy.

Cloudflare Challenge

The Challenge type handles the full-page interstitial ("Just a moment...", "Checking your browser...", I'm Under Attack mode) and invisible challenges that gate the entire site. It returns a cf_clearance cookie you replay on the next request.

A proxy is required

The solver navigates through your proxy so that the resulting cookie is valid for that proxy's egress IP. Calls without a proxy return 400. The same proxy must be used when replaying the cookie.

Request

Field	Type	Required	Notes
`type`	string	Yes	`challenge` (or alias `cloudflare-challenge`).
`url`	string	Yes	Page URL — `http`/`https`, public host, max 2048 chars.
`proxy`	string	Yes	`protocol://[user:pass@]host:port`. The cookie binds to this IP.
`user_agent`	string	No	Recommended — use the same UA you'll replay the cookie with.

Response

{
  "success": true,
  "type": "challenge",
  "cookies": { "cf_clearance": "abc123..." },
  "user_agent": "Mozilla/5.0 ...",
  "cost": 0.001
}

Some sites also return a token field instead of (or alongside) cookies — keep your code resilient to both shapes.

Field	When present	Notes
`cookies`	Always for true Challenge pages	Set on requests to the same origin.
`user_agent`	Always	Use this exact UA when replaying — Cloudflare fingerprints UAs.
`token`	Sometimes	Pass through as the form field, like a Turnstile token.

Use the result

import requests

solve = requests.post(
    "https://api.nslsolver.com/solve",
    headers={"X-API-Key": "YOUR_KEY"},
    json={
        "type": "challenge",
        "url": "https://example.com/protected",
        "proxy": "http://user:[email protected]:8080",
    },
    timeout=120,
).json()

session = requests.Session()
session.cookies.set("cf_clearance", solve["cookies"]["cf_clearance"], domain="example.com")
session.headers["User-Agent"] = solve["user_agent"]
session.proxies = {"http": "http://user:[email protected]:8080",
                   "https": "http://user:[email protected]:8080"}

# Now use `session` for downstream calls. The proxy and UA must match the solve.
session.get("https://example.com/protected")

Performance

Metric	Typical value
Solve time	1-5 seconds
Cookie lifetime	~300 seconds
Success rate	~95%

When to pick Challenge over Turnstile

Page behaviour	Use
Shows a visible widget with `data-sitekey`	Turnstile
Renders the "Just a moment..." interstitial	Challenge
Redirects through a Cloudflare challenge page before content	Challenge
No visible widget but blocks unauthenticated traffic	Challenge

Examples

import requests

r = requests.post(
    "https://api.nslsolver.com/solve",
    headers={"X-API-Key": "YOUR_KEY"},
    json={
        "type": "challenge",
        "url": "https://example.com/protected",
        "proxy": "http://user:[email protected]:8080",
    },
    timeout=120,
)
data = r.json()
print(data["cookies"]["cf_clearance"], data["user_agent"])

const r = await fetch("https://api.nslsolver.com/solve", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    "X-API-Key": process.env.NSL_API_KEY,
  },
  body: JSON.stringify({
    type: "challenge",
    url: "https://example.com/protected",
    proxy: "http://user:[email protected]:8080",
  }),
  signal: AbortSignal.timeout(120_000),
});
const { cookies, user_agent } = await r.json();

curl -X POST https://api.nslsolver.com/solve \
  -H "Content-Type: application/json" \
  -H "X-API-Key: $NSL_API_KEY" \
  -d '{
    "type": "challenge",
    "url": "https://example.com/protected",
    "proxy": "http://user:[email protected]:8080"
  }'

Troubleshooting

Symptom	Likely cause	Fix
`proxy is required`	Missing or empty `proxy`	Pass a working proxy URL.
`cf_clearance` rejected on first request	Different proxy used for replay	Use the same proxy for solve and downstream traffic.
`cf_clearance` rejected after a while	Cookie expired	Re-solve. The cookie is short-lived.
Repeated 503	Proxy is on a Cloudflare blocklist	Try residential or a different datacenter range.

Cloudflare Challenge

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