curl
curl •
Since 1998
Quick Actions
Official Docs
What is curl?
curl is a command-line tool and library for transferring data with URLs. Supporting numerous protocols, curl is ubiquitous in development, testing, and automation. While primarily used for API testing and file transfers, curl appears in web server logs when developers test endpoints or automate tasks. The tool's flexibility and widespread availability make it a fundamental part of modern web development. curl is often used in scripts, CI/CD pipelines, and monitoring systems, making its user agent a common sight in server logs.
User Agent String
curl/7.81.0
How to Control curl
Block Completely
To prevent curl from accessing your entire website, add this to your robots.txt file:
# Block curl
User-agent: curl
Disallow: /
Block Specific Directories
To restrict access to certain parts of your site while allowing others:
User-agent: curl
Disallow: /admin/
Disallow: /private/
Disallow: /wp-admin/
Allow: /public/
Set Crawl Delay
To slow down the crawl rate (note: not all bots respect this directive):
User-agent: curl
Crawl-delay: 10
How to Verify curl
Verification Method:
User agent string with curl version
User agent string with curl version
Learn more in the official documentation.
Detection Patterns
Multiple ways to detect curl in your application:
Basic Pattern
/curl/i
Strict Pattern
/^curl/7\.81\.0$/
Flexible Pattern
/curl[\s\/]?[\d\.]*?/i
Vendor Match
/.*curl.*curl/i
Implementation Examples
// PHP Detection for curl
function detect_curl() {
$user_agent = $_SERVER['HTTP_USER_AGENT'] ?? '';
$pattern = '/curl/i';
if (preg_match($pattern, $user_agent)) {
// Log the detection
error_log('curl detected from IP: ' . $_SERVER['REMOTE_ADDR']);
// Set cache headers
header('Cache-Control: public, max-age=3600');
header('X-Robots-Tag: noarchive');
// Optional: Serve cached version
if (file_exists('cache/' . md5($_SERVER['REQUEST_URI']) . '.html')) {
readfile('cache/' . md5($_SERVER['REQUEST_URI']) . '.html');
exit;
}
return true;
}
return false;
}
# Python/Flask Detection for curl
import re
from flask import request, make_response
def detect_curl():
user_agent = request.headers.get('User-Agent', '')
pattern = r'curl'
if re.search(pattern, user_agent, re.IGNORECASE):
# Create response with caching
response = make_response()
response.headers['Cache-Control'] = 'public, max-age=3600'
response.headers['X-Robots-Tag'] = 'noarchive'
return True
return False
# Django Middleware
class curlMiddleware:
def __init__(self, get_response):
self.get_response = get_response
def __call__(self, request):
if self.detect_bot(request):
# Handle bot traffic
pass
return self.get_response(request)
// JavaScript/Node.js Detection for curl
const express = require('express');
const app = express();
// Middleware to detect curl
function detectcurl(req, res, next) {
const userAgent = req.headers['user-agent'] || '';
const pattern = /curl/i;
if (pattern.test(userAgent)) {
// Log bot detection
console.log('curl detected from IP:', req.ip);
// Set cache headers
res.set({
'Cache-Control': 'public, max-age=3600',
'X-Robots-Tag': 'noarchive'
});
// Mark request as bot
req.isBot = true;
req.botName = 'curl';
}
next();
}
app.use(detectcurl);
# Apache .htaccess rules for curl
# Block completely
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} curl [NC]
RewriteRule .* - [F,L]
# Or redirect to a static version
RewriteCond %{HTTP_USER_AGENT} curl [NC]
RewriteCond %{REQUEST_URI} !^/static/
RewriteRule ^(.*)$ /static/$1 [L]
# Or set environment variable for PHP
SetEnvIfNoCase User-Agent "curl" is_bot=1
# Add cache headers for this bot
<If "%{HTTP_USER_AGENT} =~ /curl/i">
Header set Cache-Control "public, max-age=3600"
Header set X-Robots-Tag "noarchive"
</If>
# Nginx configuration for curl
# Map user agent to variable
map $http_user_agent $is_curl {
default 0;
~*curl 1;
}
server {
# Block the bot completely
if ($is_curl) {
return 403;
}
# Or serve cached content
location / {
if ($is_curl) {
root /var/www/cached;
try_files $uri $uri.html $uri/index.html @backend;
}
try_files $uri @backend;
}
# Add headers for bot requests
location @backend {
if ($is_curl) {
add_header Cache-Control "public, max-age=3600";
add_header X-Robots-Tag "noarchive";
}
proxy_pass http://backend;
}
}
Should You Block This Bot?
Recommendations based on your website type:
| Site Type | Recommendation | Reasoning |
|---|---|---|
| E-commerce | Optional | Evaluate based on bandwidth usage vs. benefits |
| Blog/News | Allow | Increases content reach and discoverability |
| SaaS Application | Block | No benefit for application interfaces; preserve resources |
| Documentation | Selective | Allow for public docs, block for internal docs |
| Corporate Site | Limit | Allow for public pages, block sensitive areas like intranets |
Advanced robots.txt Configurations
E-commerce Site Configuration
User-agent: curl
Crawl-delay: 5
Disallow: /cart/
Disallow: /checkout/
Disallow: /my-account/
Disallow: /api/
Disallow: /*?sort=
Disallow: /*?filter=
Disallow: /*&page=
Allow: /products/
Allow: /categories/
Sitemap: https://example.com/sitemap.xml
Publishing/Blog Configuration
User-agent: curl
Crawl-delay: 10
Disallow: /wp-admin/
Disallow: /drafts/
Disallow: /preview/
Disallow: /*?replytocom=
Allow: /
SaaS/Application Configuration
User-agent: curl
Disallow: /app/
Disallow: /api/
Disallow: /dashboard/
Disallow: /settings/
Allow: /
Allow: /pricing/
Allow: /features/
Allow: /docs/
Quick Reference
User Agent Match
curl
Robots.txt Name
curl
Category
other
Respects robots.txt
May not respect
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