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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchUse curl_cffi as a requests-compatible HTTP client, and pass impersonate="chrome" (or another supported browser profile) when a site treats Python’s default TLS/HTTP fingerprint differently from a real browser. Install it with pip install curl_cffi --upgrade. The current project guidance supports Python 3.10 and newer.
Impersonation changes transport-level fingerprints; it does not run JavaScript, solve every CAPTCHA, or guarantee access to a protected site. A reliable scraper combines an appropriate profile with sessions, conservative concurrency, proxy handling, retries, and respect for the target’s terms and robots guidance.
Install curl_cffi and make a first request
Create or activate a Python 3.10+ virtual environment, then upgrade the package:
python -m pip install --upgrade curl_cffiThe requests-like API is exposed from curl_cffi.requests:
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from curl_cffi import requests
response = requests.get(
"https://example.com",
impersonate="chrome",
timeout=30,
)
print(response.status_code)
print(response.text[:200])The unversioned chrome, safari, and safari_ios names follow the latest profile available in the installed package. That makes them convenient defaults, but an update can change the exact browser version they represent.
Choose a browser profile
Many blocks are triggered before a page is returned, when a server evaluates the TLS ClientHello, HTTP/2 settings, header ordering, and related signals. curl_cffi can impersonate those browser signatures or JA3 fingerprints instead of presenting the usual Python-client fingerprint.
| Profile choice | When to use it | Important qualification |
|---|---|---|
chrome |
General-purpose Chrome-like traffic | Tracks the newest built-in Chrome profile shipped by your installed version |
| Versioned Chrome profile | A target expects a specific browser generation | Pin and retest after package upgrades |
safari or safari_ios |
Testing Safari-family fingerprints | These are transport profiles, not Safari’s rendering engine |
| Another built-in target | The target guide lists a matching browser family | Use the exact name supported by your installed release |
Start with a built-in profile. Custom ja3, akamai, and extra_fp values are intended for a documented target fingerprint; guessing them can make traffic less consistent, not more legitimate.
Build a small scraper with sessions
A session keeps cookies and connection state between requests. It is preferable to creating a new connection for every URL and is the natural place to set shared headers, a profile, and a timeout.
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URLS = [
"https://example.com/",
"https://example.com/about",
]
with requests.Session() as session:
session.impersonate = "chrome"
session.headers.update({
"Accept": "text/html,application/xhtml+xml",
"Accept-Language": "en-US,en;q=0.9",
})
for url in URLS:
response = session.get(url, timeout=30)
response.raise_for_status()
print(url, len(response.content))
print(response.text[:120])If your installed release does not accept a session-level impersonate assignment, pass impersonate="chrome" on each request instead. Always check the response URL and status code after redirects; a successful HTTP response can still be a login page, consent page, or block page.
Cookies and custom headers
Supply known cookies with the cookies mapping, or let a session retain cookies set by earlier responses:
from curl_cffi import requests
cookies = {"region": "us"}
headers = {"User-Agent": "your-application-name/1.0"}
response = requests.get(
"https://example.com/data",
impersonate="chrome",
cookies=cookies,
headers=headers,
timeout=30,
)
print(response.status_code)Do not claim to be a different product or user agent than your application actually is. Keep authentication credentials in environment variables or a secret manager rather than source code.
Use HTTP and SOCKS proxies
curl_cffi accepts a proxy mapping. The documented pattern is:
from curl_cffi import requests
proxies = {
"https": "http://localhost:3128",
}
response = requests.get(
"https://example.com",
impersonate="chrome",
proxies=proxies,
timeout=30,
)
print(response.status_code)Add an http entry when your scraper also requests plain HTTP URLs. SOCKS proxy URLs are supported as well; use the scheme and credentials supplied by your proxy operator. Rotate addresses only when you have a legitimate operational reason, and keep request rates low enough for the site and your proxy service.
Add timeouts and retries without creating a request storm
Set a finite timeout on every network call. A retry should handle transient transport failures and selected server responses, not repeatedly hammer a page that is returning a deliberate denial. Exponential backoff with a cap gives a target time to recover.
import time
from curl_cffi import requests
RETRYABLE_STATUS = {408, 425, 429, 500, 502, 503, 504}
def fetch(url, attempts=4):
last_error = None
for attempt in range(attempts):
try:
response = requests.get(
url,
impersonate="chrome",
timeout=30,
)
if response.status_code not in RETRYABLE_STATUS:
response.raise_for_status()
return response
last_error = RuntimeError(f"HTTP {response.status_code}")
except Exception as exc:
last_error = exc
if attempt + 1 < attempts:
time.sleep(min(2 ** attempt, 16))
raise last_error
page = fetch("https://example.com")
print(page.text[:200])The project also advertises native retry support. If you use that facility, read the version’s API documentation and configure limits, backoff, and retryable conditions explicitly. Never retry authentication failures, persistent 403 responses, or a CAPTCHA page as if they were network outages.
Use asynchronous requests for larger crawls
For I/O-bound work, curl_cffi provides an asyncio interface through AsyncSession. Bound concurrency with a semaphore; unbounded tasks can exhaust file descriptors, overload a target, or trigger rate limits.
import asyncio
from curl_cffi import requests
URLS = [
"https://example.com/",
"https://example.com/about",
"https://example.com/contact",
]
async def fetch_one(session, url, gate):
async with gate:
response = await session.get(
url,
impersonate="chrome",
timeout=30,
)
response.raise_for_status()
return url, response.status_code, response.text
async def main():
gate = asyncio.Semaphore(5)
async with requests.AsyncSession() as session:
results = await asyncio.gather(
*(fetch_one(session, url, gate) for url in URLS),
return_exceptions=True,
)
for result in results:
print(result[0:2] if not isinstance(result, Exception) else result)
asyncio.run(main())Async requests can use proxy rotation, and the project feature list includes HTTP/2, HTTP/3, WebSockets, and retry support. Availability and option names can vary by installed release, so pin a tested version and verify those settings against that release before deploying a crawler. Concurrency is not a license to ignore robots instructions or a site’s published limits.
Understand what impersonation can and cannot do
What it changes
- TLS signatures and JA3-style fingerprints can resemble a supported browser.
- HTTP behavior associated with that profile can be negotiated instead of the default Python-client behavior.
- Sessions, cookies, headers, and proxies can then be layered on the same request.
What it does not change
- curl_cffi is not a full browser and does not execute page JavaScript or render a DOM.
- It cannot guarantee that a particular anti-bot provider will allow access.
- It does not solve CAPTCHAs, account challenges, device reputation, or an IP block by itself.
If a page is assembled only after JavaScript runs, use an authorized browser-automation workflow or an official API instead of expecting a transport fingerprint to produce the rendered data.
Inspect responses before extracting data
Do not treat status_code == 200 as proof that you received the intended document. Check the content type, final URL, size, and a distinctive marker from the page.
from curl_cffi import requests
response = requests.get(
"https://example.com",
impersonate="chrome",
timeout=30,
allow_redirects=True,
)
content_type = response.headers.get("content-type", "")
print("status:", response.status_code)
print("final URL:", response.url)
print("content type:", content_type)
if "text/html" not in content_type.lower():
raise ValueError("Expected HTML")
if "Example Domain" not in response.text:
raise ValueError("Unexpected page or block response")Save a small diagnostic sample (status, headers, final URL, and the first few hundred bytes) rather than logging cookies or authorization headers. This makes block pages and redirects distinguishable without leaking credentials.
Troubleshoot common failures
| Symptom | Likely cause | Fix |
|---|---|---|
| ImportError or installation failure | Python is older than the supported 3.10 baseline, or the environment is not the one where pip installed the package | Run python --version, activate the intended environment, and reinstall with python -m pip install --upgrade curl_cffi |
| 403 or an interstitial block | IP reputation, rate, missing cookies, account policy, or a fingerprint that does not match the target | Reduce concurrency, use a permitted proxy, preserve the normal session flow, try a supported profile, and stop if the site requires a challenge |
| 429 responses | Requests are arriving too quickly | Honor Retry-After when present, add capped backoff, and lower concurrency |
| 200 response containing “verify you are human” | You received a challenge page, not the requested content | Detect the marker, do not parse it as data, and use an authorized browser or API path |
| Timeouts | Slow origin, proxy failure, DNS/connectivity issue, or a page waiting on browser execution | Set a finite timeout, retry only transient errors, test without the proxy, and confirm whether the endpoint actually needs JavaScript |
| Data differs from a browser | JavaScript rendering, client-side API calls, cookies, geolocation, or user-agent variation | Inspect network behavior, supply legitimate cookies or headers, or switch to browser automation/API access |
| Custom fingerprint still blocked | The supplied JA3/Akamai/extra fingerprint is incomplete, stale, or inconsistent with other headers | Prefer a maintained built-in profile; use custom values only when you have a documented target fingerprint |
Performance, reliability, and maintenance
- Reuse connections: a session reduces setup overhead and preserves cookies, but separate sessions are useful when identities must not share state.
- Control concurrency: begin with a small semaphore and increase only after observing latency, errors, and the target’s guidance.
- Pin and update deliberately: unversioned profiles follow the latest available fingerprint, while versioned profiles improve repeatability. Test profile changes before production rollout.
- Measure the right outcomes: record latency, status, final URL, response size, retry count, and the proportion of pages that are actually data rather than challenge HTML.
- Cache responsibly: avoid downloading unchanged resources repeatedly, while respecting freshness requirements and access rules.
- Use an official interface when available: it is usually more stable than scraping a presentation page and avoids unnecessary load.
Or skip the browser setup
If your goal is a clean visual capture rather than HTML data extraction, ScreenshotNeo is a website screenshot API and MCP server. One GET request returns a PNG, JPEG, WebP, or PDF. Before capture it accepts the consent banner like a visitor and removes more than 60 known consent platforms, newsletter popups, and chat widgets; each cleanup step can be disabled. Bot checks, CAPTCHAs, blank pages, timeouts, failed loads, and cache hits cost nothing, and the response reports the result in X-Page-Verdict and X-Billed headers. Its MCP tools—take_screenshot, get_page_info, and capture_pdf—let Claude, Cursor, or another MCP client request captures.
See the ScreenshotNeo API documentation for all options. A Python call is:
import requests
r = requests.get(
"https://api.screenshotneo.com/v1/shot",
params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"},
timeout=90,
)
open("shot.webp", "wb").write(r.content)The equivalent cURL request is:
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpFrom Node.js:
const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://stripe.com' });
const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);ScreenshotNeo also supports full-page and element captures, lazy-image loading, dark mode, device presets, custom viewports, retina scale, PDF paper settings and page ranges, HTML/CSS input, custom JavaScript, clicks, selector waits, delays, network-idle waits, request blocking, headers, cookies, user agents, authorization, timezone, geolocation, transparent backgrounds, resizing, chosen cache TTLs, signed links, asynchronous webhooks, bulk capture of up to 100 URLs per call, a usage API, and an OpenAPI specification. Parameters commonly used by other screenshot APIs are accepted to ease migration.
| Plan | Included screenshots/month | Price |
|---|---|---|
| Free | 1,000 | $0, no card |
| Starter | 3,000 | $5 |
| Growth | 15,000 | $15 |
| Pro | 60,000 | $39 |
| Scale | 250,000 | $99 |
| Business | 1,000,000 | $249 |
Every feature is included on every plan; annual billing provides two months free. Create a free ScreenshotNeo account to get 1,000 screenshots a month without a card.
Frequently Asked Questions
When should I use a versioned profile instead of chrome?
Use a versioned profile when you need repeatable fingerprint behavior for a documented target. The unversioned name follows the newest profile shipped by your installed release, so upgrades can change it.
Can curl_cffi replace browser automation for every site?
No. It changes HTTP/TLS fingerprints but does not execute JavaScript or provide a browser’s rendering and interaction environment. Choose an authorized browser workflow or API when the site depends on those capabilities.
What should I do with a custom JA3 or Akamai fingerprint?
Treat it as a target-specific configuration. Use ja3, akamai, and extra_fp only when the fingerprint is documented and maintained; otherwise begin with a built-in browser profile.
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