2Factor.in OTP API vs Bird Verify

2Factor.in OTP API has no write-up on Specifiction yet; its figures are above.

Bird Verify confirms control of a phone number or email address by sending a code and checking the recipient’s response. It supports SMS, email, WhatsApp, voice and channel orchestration, with voice OTP described as rolling out. Eligible fallback delivery can send another code through a different channel while preserving verification and expiry. Bird says codes use a cryptographic random source, are stored as HMAC-SHA256 hashes and compared in constant time. Each session allows a bounded number of checks, five by default; per-recipient send caps and resend cooldowns also apply. Phone numbers must use international format, and requests cannot select channels unavailable in a country configuration. WhatsApp verification uses a Bird-managed business number and authentication template, with restrictions in some countries. Developers can use Node.js, Python, Go, PHP, cURL, CLI or MCP. The free Verify plan has no separate verification fee, but channel-message charges apply. API and web platforms include workspace controls, roles and audit logs.