Cap

Best CAPTCHA Alternatives for 2026 ​

Short answer: the best CAPTCHA alternative depends on what you're optimizing for. Cap, an open-source, self-hosted proof-of-work CAPTCHA, is best for teams that want privacy-first protection with no per-request fees. Cloudflare Turnstile is best if you're already on Cloudflare and want zero hosting. FriendlyCaptcha is best if you want a paid, managed, EU-hosted proof-of-work service. ALTCHA is best if you want a minimal open-source proof-of-work library with nothing else attached.

Cap is a free, open-source CAPTCHA alternative that replaces visual puzzles with proof-of-work and instrumentation challenges, self-hosted as a single Docker container.

Full disclosure

This page lives in Cap's documentation, so we obviously have a favorite. The criteria are laid out below so you can weigh them yourself, and where a competitor is the better fit, we say so.

Comparison at a glance ​

ProductBest forOpen sourceSelf-hostedPrivacy-firstFree at scaleUXBot resistance
CapFull control, privacy, $0✅ Apache 2.0✅✅✅Checkbox, no puzzlesPoW + instrumentation
Cloudflare TurnstileCloudflare-native stacks❌❌🟨 fingerprinting✅Invisible, but error-proneNetwork signals
ALTCHAMinimal OSS library✅ MIT (widget)✅✅✅Checkbox, no puzzlesPoW only (OSS tier)
FriendlyCaptchaManaged EU PoW service🟨 clients only❌✅❌ quotasInvisible/checkboxPoW only
hCaptchaEnterprise, puzzle-tolerant❌❌🟨🟨Image puzzlesHigh, at UX cost
reCAPTCHAGoogle-integrated stacks❌❌❌🟨Puzzles / risk scoreMixed
SilentShieldWordPress, managed invisible❌❌🟨 behavioral❌ 500 req/mo freeInvisibleBehavioral model

The full 12-criteria matrix (error rates, GDPR, customization, RSW support and more) is on the feature comparison page.

The alternatives, ranked ​

1. Cap ​

Cap is an open-source (Apache 2.0), self-hosted CAPTCHA that makes automation expensive instead of guessing who's human. Users click one checkbox; a proof-of-work challenge runs silently in their browser while instrumentation challenges verify the environment is a real browser.

  • Best for: teams that want full control, real privacy, and no bill at any traffic volume.
  • Key strengths: two independent verification layers (PoW + instrumentation), ~20 KB widget, deterministic difficulty you control per site key, reCAPTCHA-compatible /siteverify API, dashboard with multi-site-key management, works in Brave, Librewolf, and Tor Browser.
  • Tradeoffs: you host it (one Docker container plus Valkey; a $5 VPS covers most sites). If you refuse to run any backend service, a managed option fits better.
  • Privacy: no cookies, no fingerprinting, no third-party calls. Data never leaves your servers. See Compliance.

Quickstart →

2. Cloudflare Turnstile ​

Turnstile is Cloudflare's free CAPTCHA replacement, running invisible challenges that lean on Cloudflare's network signals and browser fingerprinting.

  • Best for: sites already routing traffic through Cloudflare that want zero hosting.
  • Key strengths: free, fully managed, invisible for most users, easy integration.
  • Tradeoffs: closed source, no self-hosting, and no override when Cloudflare's algorithm flags a user as suspicious, which is widely reported for privacy browsers and VPN users. The verdict is theirs, not yours.
  • Privacy: better than reCAPTCHA, but the client talks to challenges.cloudflare.com on every load and relies on fingerprinting signals.

Full comparison: Cap vs Turnstile →

3. ALTCHA ​

ALTCHA is the closest open-source project to Cap in spirit: proof-of-work, no fingerprinting, no third party.

  • Best for: developers who want a minimal, library-style PoW widget with no separate service.
  • Key strengths: open source (MIT widget), self-hostable, GDPR-friendly, well documented.
  • Tradeoffs: PoW only in the open-source tier (the ML-based second layer requires the paid Sentinel product), ~34 KB widget, no standalone server or dashboard out of the box.

Full comparison: Cap vs ALTCHA →

4. FriendlyCaptcha ​

An early proof-of-work CAPTCHA, now a hosted commercial service focused on EU privacy compliance.

  • Best for: teams that want a vendor with a contract, SLA, and EU hosting, and whose traffic fits a paid tier.
  • Key strengths: clean PoW model, GDPR-friendly, accessible widget, no puzzles.
  • Tradeoffs: the server is proprietary and there's no self-hosting. Pricing starts at €9/month for 1,000 requests/month and scales with volume.

Full comparison: Cap vs FriendlyCaptcha →

5. SilentShield ​

A hosted, invisible bot-protection service by German company Forge12, distributed mainly as a WordPress plugin. Detection is behavioral: per Forge12, an AI model scores interaction patterns such as mouse, keyboard, scroll, and timing.

  • Best for: WordPress sites that want plug-and-play invisible protection and accept a request quota.
  • Key strengths: invisible for most users, EU servers, first-party plugins for CF7, WPForms, Elementor, and WooCommerce, and a small client (stated as under 10 KB).
  • Tradeoffs: closed source, no self-hosting, free tier capped at 500 requests/month (paid tiers from €9/month for 5,000). Behavioral classification is probabilistic, and bots that imitate human input target the classifier directly; unlike proof-of-work, this approach does not impose a computational cost floor on attackers.

Full comparison: Cap vs SilentShield →

6. hCaptcha ​

reCAPTCHA's main commercial rival, built on image-labeling puzzles.

  • Best for: enterprises that need aggressive protection and accept the UX cost.
  • Key strengths: strong bot resistance, enterprise features, compliance options.
  • Tradeoffs: users hate puzzles, and drop-off on hCaptcha challenges can reach 5-15% depending on difficulty. The free tier serves puzzles aggressively.

Full comparison: Cap vs hCaptcha →

7. reCAPTCHA ​

Google's incumbent, in v2 ("I'm not a robot") and v3 (invisible, score-based) flavors.

  • Best for: stacks already deep in Google's ecosystem.
  • Key strengths: ubiquitous, familiar, free for moderate volumes.
  • Tradeoffs: sends user data to Google, 500 KB+ client, v2's puzzles are increasingly easy for AI and hard for humans, v3 silently penalizes VPN and privacy-browser users, and Enterprise is metered per assessment.

Full comparison: Cap vs reCAPTCHA → · Migration guide →

Also worth knowing ​

  • Anubis: a proof-of-work scraper deterrent for gating entire sites at the proxy level rather than a form CAPTCHA. Cap vs Anubis →
  • mCAPTCHA: an open-source (AGPL-3.0 core) proof-of-work CAPTCHA that pioneered variable-difficulty PoW and ships its own standalone server. It remains pre-1.0 with a slow release cadence, its widget bundle is larger than Cap's or ALTCHA's, and the AGPL license complicates commercial embedding. Full breakdown →

More options (MTCaptcha, GeeTest, Arkose Labs) are covered on the feature comparison page.

How do you choose a CAPTCHA alternative? ​

  1. Do you refuse to host anything? Turnstile (free, Cloudflare verdicts) or FriendlyCaptcha (paid, EU, PoW).
  2. Do you want open source and control? Cap, either as a full standalone server with a dashboard or as a minimal server library; ALTCHA is another solid library-only option.
  3. Is conversion your top metric? Avoid anything with image puzzles. See CAPTCHA and conversion rate.
  4. Mostly mobile traffic? See bot protection for mobile forms.
  5. WordPress with low traffic? SilentShield's plugin is convenient; Cap works there too via community integrations without the quota.

FAQ ​

What is the best CAPTCHA alternative? ​

It depends on your priorities. Cap is the best fit for open-source, self-hosted, privacy-first protection with no fees. Turnstile fits Cloudflare-native stacks, FriendlyCaptcha fits teams that want a managed EU PoW vendor, and ALTCHA fits minimalists.

What is the best open-source CAPTCHA alternative? ​

Cap and ALTCHA. Cap adds a standalone server, dashboard, instrumentation challenges, and a reCAPTCHA-compatible API on top of proof-of-work; ALTCHA stays a lean library. See open-source CAPTCHA options.

What is the best self-hosted CAPTCHA? ​

Cap. A small Docker deployment, a web dashboard, multi-site-key support, and no third-party round-trip. Nothing about your visitors leaves your servers. Quickstart →

Which CAPTCHA alternative is best for privacy? ​

Self-hosted proof-of-work options, because they need no fingerprinting or behavioral profiling. Cap sets no cookies and sends nothing to any vendor, and it doesn't penalize Brave, Librewolf, Tor, or VPN users.

Which CAPTCHA alternative has the best user experience? ​

Anything without visual puzzles. Cap shows a single checkbox with a live progress indicator; Turnstile and SilentShield are invisible for users their models classify as human; hCaptcha and reCAPTCHA v2 still drop users into image challenges.

What is the best invisible CAPTCHA? ​

Turnstile and SilentShield are invisible by default but rely on fingerprinting or behavioral scoring, so misclassified users get blocked with no recourse. Cap's floating and programmatic modes are invisible until submit while staying deterministic: every real user has a guaranteed path through.

Is Cap a good alternative to reCAPTCHA? ​

Yes. The /siteverify API is compatible with reCAPTCHA's shape, so server-side migration is mostly a URL swap, and you can run both side by side during cut-over. Unlike reCAPTCHA, Cap is open source, self-hosted, and never shows image puzzles. See the migration guide.

See also ​