AdvancedCaptcha | Modern Hub Captcha System [1.21.11]

AdvancedCaptcha 1.3-Beta
Modern Hub Captcha System for Paper 1.21.11 and Java 21

Block bots and macros - Protect hub/auth servers - Button, Math, and Sequence captcha - Adaptive difficulty - Highly configurable

AdvancedCaptcha 1.3-Beta is here

AdvancedCaptcha 1.3-Beta is a major modernization update built for modern Paper servers. This release moves the plugin to Paper 1.21.11 and Java 21, adds a new sequence captcha, introduces adaptive difficulty, improves anti-bot traps, and fixes several runtime issues from older builds.

If you use AdvancedCaptcha on a hub, lobby, auth, survival, or minigame network, this update gives you a stricter and more reliable verification layer before players can interact with the server.

What is AdvancedCaptcha?

AdvancedCaptcha verifies players when they join your server. Until verification is complete, the player can be frozen and prevented from moving, chatting, using blocked commands, interacting with the world, opening inventories, dropping or picking up items, swapping hands, and attacking.

The goal is simple: keep automated bots and basic macros away while keeping the captcha flow clear for real players.

Main Features

• Button Captcha - Players click the correct colored text button.
• Math Captcha - Players solve addition, subtraction, or multiplication challenges.
• Sequence Captcha - New in 1.3-Beta. Players click a generated color sequence in the correct order.
• Random Captcha Mode - Choose from a configurable captcha pool.
• Adaptive Difficulty - Suspicious players can receive harder challenges automatically.
• Decoy Traps - Wrong button options can look similar to the correct answer to catch simple scripts.
• Freeze System - Blocks player actions before captcha completion.
• Allowed Auth Commands - Keep commands like /login and /register usable during verification.
• Multilingual Messages - English, Russian, and Ukrainian included.
• Sounds and Particles - Configurable feedback for success and failure.
• Admin Commands - Reload configuration and reset a player's verification state.
• Permission Bypass - Let trusted players or staff skip captcha checks.

New in 1.3-Beta

Sequence Captcha

• Adds ordered color-click challenges.
• Configurable minimum and maximum sequence length.
• Optional unique colors per sequence.
• Optional progress reset after a wrong click.

Adaptive Difficulty

• Tracks in-memory player and IP suspicion scores.
• Wrong answers, fast clicks, and timeouts can increase suspicion.
• Successful captcha completion can reduce suspicion.
• Suspicious and high-risk players can receive harder captcha pools.

Stronger Button Captcha

• Wrong options can use the same text with a different color.
• Wrong options can use the same color with different text.
• Case variants can be used as traps where supported by the language.
• The correct answer is still guaranteed.

Safer Runtime Behavior

• Secure random tokens are used for captcha sessions.
• Internal /captcha_click values are parsed and validated safely.
• Old delayed captcha buttons are prevented from affecting refreshed sessions.
• Player id, session token, button index, and IP are checked before accepting a click.
• Captcha cleanup now uses safe main-thread Bukkit API access.

Commands

/advancedcaptcha reload

Reloads configuration and message files.

/advancedcaptcha reset [player]

Clears captcha state and starts a new captcha for an online player. Useful for testing and support.

/acaptcha reload

Short alias for reload.

/acaptcha reset [player]

Short alias for reset.

/captcha_click is an internal command used by clickable captcha buttons and should not be used manually.

Permissions

• advancedcaptcha.admin

  - Allows using AdvancedCaptcha administration commands. Default: OP.

• advancedcaptcha.bypass

  - Skips captcha verification. Default: false.

Important: AdvancedCaptcha 1.2-SNAPSHOT targeted Minecraft 1.16.5 to 1.21.5. AdvancedCaptcha 1.3-Beta is a modern Paper 1.21.11 release and should be treated as a new compatibility line.

Secure your hub with a clean, modern, and configurable captcha system.