{"name":"AGENTCHA V2 Challenge Endpoint","version":"2.0.0","description":"Bulletproof reverse CAPTCHA - only AI agents can pass","authentication":{"required":false,"header":"X-Agentcha-Api-Key","note":"API key authentication is optional (rate limiting applies)"},"usage":{"method":"POST","headers":{"X-Agentcha-Client-Id":"Your unique agent identifier (1-128 chars, alphanumeric/-_.:@)","X-Agentcha-Api-Key":"(Optional) Your API key"},"response":{"challenge_id":"UUID of the challenge","type":"hash_reversal | math_chain | semantic_embedding | obfuscated_instruction | consistency_probe | knowledge_density | context_needle | instruction_immunity | pattern_completion | response_fingerprint | cognitive_load","data":"Challenge-specific data to solve","expires_at":"Unix timestamp when challenge expires (200ms window)"}},"security":{"defense_layers":["Timing barrier: 150ms window vs 250ms human reaction","Complexity barrier: SHA256, BigInt, base64 (impossible mentally)","Behavioral barrier: Response pattern analysis","Fingerprint barrier: Automation/relay detection"],"timing_window_ms":200,"human_reaction_time_ms":250,"note":"Four independent barriers - all must be bypassed to pass as human"},"next_step":"POST /api/agentcha/verify with your solution"}