Legal documents with certified electronic signature for Mexico
Biometric handwritten signature, SAT e.firma and NOM-151 stamping with an authorized PSC. One API, one dashboard and one link so your customers sign contracts, promissory notes and agreements with full legal validity in Mexico.
Built for companies that sign hundreds of documents per month
The signature level each document needs
From a simple OTP for terms and conditions, to SAT e.firma for binding contracts before authorities. Combine them in the same document.
Biometric handwritten signature
On-screen handwritten stroke + selfie with liveness detection + face match. The most robust biometric evidence for commercial contracts, promissory notes and labor agreements.
SAT e.firma (FIEL)
SAT digital certificate (.cer + .key). Legally equivalent to a handwritten signature for all purposes. The choice when you need binding signature before tax or judicial authorities.
How it works
From a PDF to a legally sealed document in four steps.
Upload the document
Upload a PDF or use a reusable template. The API also accepts plain text or HTML for dynamic generation.
Define signers
One or many signers, optionally with sequential order. Assign signature type per signer (simple, biometric or e.firma).
Collect signatures
Each signer gets a unique link by email/WhatsApp. Sign from mobile without downloading anything. Automatic reminders.
NOM-151 sealing
When all sign, we seal the PDF with an authorized PSC: SHA-256 hash + certified timestamp. Webhook with the certificate.
Your document, sealed by an authorized PSC.
NOM-151 is the only technical method recognized in Mexico that guarantees a document existed exactly as is on a specific date. Without this, a judge can question document integrity.
SHA-256 hash of signed PDF, immutably linked to content.
Certified timestamp (RFC 3161) issued by a recognized authority.
PSC authorized by the Ministry of Economy — the only official path.
Downloadable PDF certificate, admissible in court without further procedures.
Hash the signed PDF
We compute the SHA-256 hash of the document with all signatures embedded.
Request to PSC
We send the hash to an authorized PSC, which applies an RFC 3161 timestamp.
Certified record
You receive a PDF with NOM-151 stamping, valid as legal evidence in any Mexican court.
Sign with your taxpayers' SAT e.firma
e.firma (formerly FIEL) is the digital certificate the SAT issues to individuals and companies. Signing with it is the closest thing to a handwritten signature in Mexican digital law.
Maximum legal validity — equivalent to handwritten signature per Code of Commerce.
We validate certificate validity against SAT before signing.
User uploads .cer, .key and password — we never persist the private key.
Compatible with any flow: B2B contracts, mandates, digital notarized powers.
Compare our signature types
Each level has its place. This helps you pick.
| Feature | Biometric | SAT e.firma |
|---|---|---|
| IP, device and timestamp capture | ✓ | ✓ |
| Legal validity | ✓✓ | ✓✓✓ |
| Evidence type | Stroke + selfie + liveness | SAT digital certificate |
| Biometric signer verification | ✓ | ✓ |
| SAT validation | — | ✓ |
| NOM-151 sealing available | ✓ | ✓ |
Use cases
What Mexican companies sign with Singula every day.
Promissory notes
Biometric signature + NOM-151. Valid for collections and executive commercial trial.
Lease agreements
Tenant and landlord sign from mobile. NOM-151 certificate included.
B2B service contracts
Multi-signer with sequential order. e.firma for binding agreements.
Internal agreements
For companies with high internal signing volume. Reusable templates.
Academic agreements
Enrollments, scholarships and collaboration agreements. Easy for the student.
Medical consents
Biometric signature + patient selfie. Meets COFEPRIS requirements.
Designed for every team in your company
Each department has different flows. Singula adapts without forcing you to change how you work.
Legal
Binding contracts with SAT e.firma, NOM-151 stamping and forensic audit trail for court.
Sales
Accelerate close with templates, automatic reminders and signing from the customer's mobile.
Human resources
Paperless onboarding. Biometric signature with selfie + liveness to validate the employee.
Finance
Court-collectible documents with biometric signature and NOM-151 certificate included.
Ready-made templates for the most common Mexican contracts
Start with a legally-vetted template or upload your own. Dynamic variables to personalize on the fly.
Built for real workflows
Beyond simple "upload and sign". Everything you need to operate at scale.
Multi-signer with order
Define who signs first. Next signer only gets the link when previous one is done.
Reusable templates
Upload once, use a hundred times. Dynamic variables to customize names, amounts and dates.
Live tracking
See who signed, who opened the link, who has not responded. Real-time dashboard.
Automatic reminders
Configure reminders every N days. Reduce dropoff without chasing signers manually.
Full webhook
Events for document.signed, document.completed, signer.viewed. Integrate with your CRM or ERP.
Public link or embed
Send a link via WhatsApp or embed the signing flow directly in your app via SDK.
All the evidence a judge needs.
For each signature we capture a complete evidence package: technical, biometric and temporal. All downloadable as an annex to the NOM-151 certificate.
Evidence is admissible under article 90-bis of the Code of Commerce and article 210-A of the Federal Code of Civil Procedures.
From PDF to signed contract, without a single piece of paper
Watch the full Singula flow: upload, assign signers, biometric handwritten signature, NOM-151 sealing and download the certified document. All from a dashboard, no code required.
One single call. The whole legal flow.
Upload the document, define signers with their signature types, and optionally enable NOM-151 sealing. We return unique links per signer. Webhook on completion.
curl -X POST https://api.singula.mx/v1/documents \
-H "Authorization: Bearer sk_live_..." \
-F "[email protected]" \
-F "signers[0][email][email protected]" \
-F "signers[0][type]=biometric" \
-F "signers[1][email][email protected]" \
-F "signers[1][type]=efirma" \
-F "nom151=true"
→ {
"document_id": "doc_lzk9m4ab3f",
"status": "pending_signatures",
"signers": [
{ "id": "sgn_001", "url": "https://sign.singula.mx/s/abc123", "type": "biometric" },
{ "id": "sgn_002", "url": "https://sign.singula.mx/s/def456", "type": "efirma" }
]
}
// Webhook al completar (todos firmaron + NOM-151 sellado):
{
"event": "document.completed",
"document_id": "doc_lzk9m4ab3f",
"signed_pdf_url": "https://...",
"constancia_nom151_url": "https://...",
"audit_trail": { ... }
}Connect Singula with your existing stack
Trigger signatures from your CRM, ERP or favorite automation tool. Not listed? We have webhooks and a REST API.
Constantly expanding integrations. Public roadmap at /developers.
"We used to send contracts via courier, wait for scanned signatures and archive physically. Today we close a promissory note in under 15 minutes from the customer's mobile, and the NOM-151 certificate gives us the peace of mind that every document is defensible in court."
We comply with the Mexican legal framework
Start signing legally in minutes
Contact us for early access, upload your first document and sign with your customers the same day. Direct support from our legal and technical team to clarify any doubts about legal validity.