Cap

CAPTCHA Feature Comparison: Cap vs the Alternatives ​

Cap is a free, open-source, self-hosted CAPTCHA alternative that uses proof-of-work and instrumentation challenges instead of image puzzles. Here is how it compares to reCAPTCHA, hCaptcha, Cloudflare Turnstile, Altcha, FriendlyCaptcha, SilentShield, and others across 12 criteria.

CAPTCHAOpen-sourceFreePrivateFast to solveEasy for humansSmall error rateGDPR compliantCustomizableHard for botsInstrumentationRSW supportEasy to integrate
Cap✅✅✅✅✅✅✅✅✅✅✅✅
Cloudflare Turnstile❌✅🟨🟨✅❌✅❌✅✅🟨✅
reCAPTCHA❌🟨❌❌❌🟨🟨❌🟨✅🟨✅
hCAPTCHA❌🟨🟨❌❌🟨🟨❌🟨✅🟨✅
Altcha✅✅✅✅✅✅✅✅🟨❌❌🟨
FriendlyCaptcha❌❌✅✅✅✅✅✅❌❌❌🟨
SilentShield❌🟨🟨✅✅🟨✅❌🟨✅❌✅
MTCaptcha❌🟨🟨❌❌🟨✅❌❌❌❌🟨
GeeTest❌❌❌🟨🟨🟨✅❌🟨❌❌🟨
Arkose Labs❌❌❌❌❌❌✅🟨🟨🟨🟨🟨

One criterion Cap deliberately fails: there is no managed hosting. If you refuse to run any infrastructure at all, Cloudflare Turnstile or FriendlyCaptcha is a better fit.

Note

Based on internal testing, Cap achieved lower challenge abandonment rates and higher privacy-browser compatibility than competing solutions.

"Hard for bots" refers to resistance against commodity automation, including headless browsers, scripted attacks, and self-operated bot networks. For Cap, this is primarily provided by PoW and instrumentation. This category does not consider commercial CAPTCHA-solving services or human-assisted solver platforms, as their effectiveness is difficult to independently verify.

All alternatives ​

Cloudflare Turnstile ​

Cloudflare Turnstile is a great alternative to Cap, but it is widely reported to fail or loop for users on privacy browsers such as Brave or Librewolf, because its verdicts rely on fingerprinting signals those browsers deliberately break.

Additionally, unlike Turnstile, Cap is open-source and self-hosted. With Turnstile, if Cloudflare's algorithm marks a user as "suspicious," you cannot override it. Cap puts the levers of control in your hands, so you decide the difficulty and strictness, not a third party.

Full comparison: Cap vs Cloudflare Turnstile →

reCAPTCHA ​

Not only is Cap significantly smaller and faster than reCAPTCHA, it's open-source, fully free, and much more private. Cap doesn't require you to check traffic signs or solve puzzles, and it doesn't track users or collect data.

reCAPTCHA v2 ("I'm not a robot") is getting harder for humans while remaining trivial for AI solvers (especially audio challenges). v3 (Invisible) is great, but if Google thinks you are "suspicious" (e.g., using a VPN or privacy tools), it often blocks you entirely or forces a hard puzzle loop with no way out.

Full comparison: Cap vs reCAPTCHA →

hCAPTCHA ​

Pretty much the same as reCAPTCHA, however, while it's significantly more resistant to bots, it imposes a heavy "Puzzle Tax" on your users.

Users hate puzzles. They leave. Drop-off rates on hCaptcha challenges can be 5-15% depending on difficulty. Additionally, hCaptcha's free tier is aggressive with serving puzzles to save their own costs, which hurts your conversion rates.

Full comparison: Cap vs hCaptcha →

Altcha ​

Cap is slightly smaller than Altcha and includes extra features like progress tracking, instrumentation challenges, and a simpler dashboard. If you don't need these, Altcha is still a solid choice.

Full comparison: Cap vs Altcha →

mCAPTCHA ​

While mCAPTCHA is similar to both Cap and Altcha, it is still pre-1.0 with infrequent releases and has a larger widget bundle.

FriendlyCaptcha ​

Unlike FriendlyCaptcha, Cap is completely free and self-hosted at any volume (FriendlyCaptcha's Starter plan is €9/month for 1,000 requests/month, with higher tiers as you scale).

Full comparison: Cap vs FriendlyCaptcha →

SilentShield ​

SilentShield is a hosted, invisible bot-protection service that scores mouse, keyboard, and scroll behavior instead of running a challenge. It's convenient on WordPress, but it's closed-source, can't be self-hosted, and its free tier caps at 500 requests/month (paid tiers from €9/month for 5,000 requests).

Cap imposes a real computational cost on bots rather than guessing from behavior, is fully open-source, and is free at any volume on your own infrastructure.

Full comparison: Cap vs SilentShield →

MTCaptcha ​

MTCaptcha relies heavily on image challenges, which are usually easily solvable by LLMs and OCRs and have high drop-off rates. Cap is also lightweight, self-hostable and doesn't rely on obfuscation.

GeeTest ​

Cap is free, self-hosted, and open-source, while GeeTest is a paid service. Cap is also more private and doesn't rely on tracking users or collecting data. GeeTest is also China-based, which may be a concern for some users regarding data sovereignty.

Arkose Labs ​

Arkose's CAPTCHA is known for being hard, slow, and annoying for humans to solve. It is also a paid, closed-source service mostly available to big enterprises.

They also only operate in the US, Canada, Argentina, India, Israel and a small set of other countries, excluding many EU countries.

Anubis ​

While Anubis is a great scraper deterrent and uses the same proof-of-work concept as Cap, it uses a low difficulty by default (which is easier for bots to solve) and does not provide a standalone CAPTCHA server.

Cap also implements dynamic instrumentation challenges, which make it harder for bots to finish the process after solving PoW.

Full comparison: Cap vs Anubis →