Best Verification APIs 2026
Six ways to verify a user, compared on what actually decides it — real cost by country, delivery, security, and what you're left holding afterward. Five are established OTP APIs (Twilio, Vonage, Sinch, Telesign, Auth0); Proof is the one that hands back a signed, offline-verifiable proof. Pricing from each vendor's own docs.
Every API here sends a code that carriers can lose (Microsoft has reported SMS delivery as low as 50% in some regions). Proof sidesteps delivery: the user sends the code, so no code can be lost on the way to them — from €0.0079 a proof in every country, and a signed ES256 token you keep as evidence.
One API · One key
One key does what a stack of vendors does
Every provider on this page delivers codes to phones. Proof is a single API — the same reverse-OTP flow also covers email and domains, and every verification mints a signed, offline-verifiable ES256 token for each of these:
Same price · Any asset
The same price for every asset — phone, email, and domain today, with wallet and social coming soon. No per-seat or per-MAU fees — the meters that make rivals' bills jump.
- Free every month
- 300 proofs
- Pay as you go
- €0.03 / proof
- At volume
- €0.0079 / proof on the €79 plan
Feature Matrix
Swipe to compare all 6 providers →
| Feature | Proof | Twilio | Auth0 | Vonage | Sinch | Telesign |
|---|---|---|---|---|---|---|
| Phone verification | Yes | Yes | Yes | Yes | Yes | Yes |
| Email verification | Yes | Yes | Yes | Yes | No | No |
| Domain verification | Yes | No | No | No | No | No |
| Wallet verification | Coming soon | No | No | No | No | No |
| Social verification | Coming soon | No | Yes | No | No | No |
| Reverse OTP | Yes | No | No | No | No | No |
| Proof tokens (offline) | Yes | No | OIDC only | No | No | No |
| HITL approvals | Yes | Push only | CIBA (preview) | No | No | Push (MFA) |
| MCP server | 167 tools | Alpha | No | No | Yes | No |
| Free tier | 300 proofs/mo | No | 25K MAU | No | No | No |
Pricing Comparison
Swipe for pricing notes →
| Provider | Model | Price | Free Tier | Notes |
|---|---|---|---|---|
| Proof Holdings | Per-proof (any type) | From €0.0079 | 300 proofs/mo | Same price for every proof type |
| Telesign | Per-verification | Quote-based | None | Phone SMS only. No published price; international SMS $0.05–0.50+ |
| Twilio Verify | Per-verification + fees | From $0.05 | None | Base fee + channel fees (SMS, voice). Phone + email only |
| Vonage Verify | Per-verification + fees | From €0.052 | None | Platform fee + channel fees. Phone + email |
| Sinch | Per-request | $0.01-0.06 | None | Phone only. Country-variable pricing |
| Auth0 | Per-MAU | From $35/mo | 25K MAU | Identity platform, not per-verification. Phone needs Twilio backend |
The free-tier column isn't like-for-like: Auth0's 25K counts monthly active users on an identity platform (phone sign-in still needs a Twilio backend), while Proof's 300 counts verification events. The four SMS-verification APIs have no free tier at all.
Category Winners
Proof Holdings
Only platform where one price covers phone, email, and domain — wallet and social land at the same price. €0.0079/proof on the €79 plan.
Proof Holdings
10 live channels across three asset types — Telegram, WhatsApp, SMS, magic link, DNS, HTTP and more — with OAuth and wallet signing coming soon.
Proof Holdings
167 MCP tools + HITL with cryptographic proof tokens. Twilio and Sinch have MCP servers but limited scope.
Proof Holdings
User sends code to service: no code to deliver, intercept or phish. No other platform offers this.
Proof Holdings
ES256 JWT verifiable offline. Share with third parties. Auth0 has OIDC tokens but they're session-bound.
Telesign
Negotiated US SMS rates at volume (no published price). Phone SMS only, no other asset types. Best for high-volume phone-only use cases.
Auth0
30+ social providers, enterprise SSO, SAML, LDAP. Full identity platform, not just verification.
Sinch
Missed-call OTP with caller ID. 70% faster, 25% lower cost than SMS. Android auto-intercept.
Security Comparison
All providers use HTTPS and encrypt data in transit. The key security differences are in the verification method and what happens after verification:
- No code in transit — Proof: Yes (Reverse OTP; on Telegram and WhatsApp a SIM swap alone is not enough). Others: No (an SMS code can be intercepted, phished or SIM-swapped).
- Cryptographic proof of verification — Proof: ES256 JWT. Others: Status flag only (except Auth0 OIDC).
- Offline verification — Proof: Yes (public key). Others: No.
- No identity data stored — Proof: hashed identifiers in the token, encrypted at rest. Others: Varies (Auth0 stores profiles).
Detailed Comparisons
Frequently Asked Questions
Ready to try Proof Holdings?
300 free proofs per month. No credit card required.
Building with an AI agent? The 167-tool MCP server and test mode let an agent run a real verification right now — machine quickstart in llms-full.txt.
Sources for the SMS delivery figures: Microsoft, “It's Time to Hang Up on Phone Transports for Authentication” (2020-11-10); Business Standard, “SMS scrubbing: Faulty implementation wipes out OTPs, 40% traffic disrupted” (2021-03-09).