E-signature API with SMS · 25¢ per envelope · No monthly fee

The e-signature API that sends by SMS and email in one call

Start with 25 free sandbox envelopes and send them by SMS, no card. After that it's 25¢ per envelope, flat, with text and email going out in one call.

✓No monthly fee ✓25 free sandbox envelopes ✓No credit card

You get a sandbox key on the next screen. Real delivery, not a simulation.

Check your email

We sent a sign-in link to . It is good for 15 minutes, and your sandbox key is waiting on the other side.

One field

Set delivery to both and the text goes out with the email

Send by text and email

curl -X POST https://api.esigndev.com/v1/envelopes \
  -H "Authorization: Bearer sig_sandbox_..." \
  -H "Idempotency-Key: order-41882-contract-1" \
  -H "Content-Type: application/json" \
  -d '{
    "document_name": "agreement.pdf",
    "document_base64": "JVBERi0xLjQK...",
    "delivery": "both",
    "signer": {
      "name":  "Jane Smith",
      "email": "[email protected]",
      "phone": "+18135551212"
    }
  }'

delivery takes "email", "sms" or "both". On a two-signer envelope each signer can have their own channel, so you can email the one at a desk and text the one on a roof. Text delivery is not a surcharge and it is not a fallback that fires after an email bounces. It is in the 25¢.

How it works

How SMS signing works in the e-signature API

The signer gets a link, opens it on the phone already in their hand, and signs. There is no app to install and no account for them to create.

Tag the PDF

Put ^S1 where the signature goes and ^D1 where the date goes, in white text. Invisible to the reader, findable by us.

POST it

One JSON request with the file and the signer. Delivery by email, text or both starts immediately.

Get the webhook

envelope.completed lands on your endpoint with a link to the signed PDF and its certificate.

Pricing

What it costs

What	Siglio
Per envelope	25¢
Monthly fee	$0
Per seat	$0
Minimum	$0
SMS delivery	Included, same 25¢
Sandbox	25 envelopes free, no card

You are billed when an envelope is created, not when it is signed. A declined or ignored envelope still costs 25¢.

Questions

What to check before you send contracts by text

Does the signer need an account?

No. They tap the link in the message, see the document, and sign. No app, no password, no account to create on either side.

What does a signer actually receive?

A short message naming who sent it and what it is, with a link to the signing page. When they finish, their completed copy follows by email or text.

Does SMS delivery cost more than email?

No. Email, SMS, or both in parallel is 25¢ an envelope either way. Most APIs at this price are email only, and the ones that do offer SMS usually sell it by the message.

Can I use SMS for only one of two signers?

Yes. Delivery can be set per signer, so a two-signer envelope can email the first and text the second. Signing is sequential: the second signer is not notified until the first has finished.

Is a text-message signature legally binding?

The channel a link arrives on does not change the legal standing of the signature. What matters is the record: intent to sign, attribution to a person, and a tamper-evident document. Every completed envelope carries a certificate page recording the timestamp and IP address of each event. If your use case sits near an edge, ask your own counsel rather than a vendor page.

Text yourself a contract in the next five minutes

Sandbox delivers for real. Send the first one to your own phone and see exactly what your signers see.

You get a sandbox key on the next screen. Real delivery, not a simulation.

Check your email

We sent a sign-in link to . It is good for 15 minutes, and your sandbox key is waiting on the other side.