E-signatures for developers.
$1 per envelope you send.

Send a PDF for signature with one API call. Your signer gets an email, signs on any phone in about three minutes without an account, and you get back a sealed PDF and its audit record as JSON.

Everything is on every account: embedded signing, webhooks, bulk export and an MCP server. No sales call, no go-live queue, no annual contract.

Get a test key Read the docs

Test mode is free and works the same as live. Early access is open now; self-serve signup follows.

The call

Request

curl https://api.sealpost.app/v1/envelopes \
  -H "Authorization: Bearer sk_test_4f9c…" \
  -H "Idempotency-Key: example-idempotency-key" \
  -H "Content-Type: application/json" \
  -d '{
    "title": "Merchant agreement – Blue Fern Café",
    "status": "sent",
    "files": [{ "url": "https://example.com/blue-fern-agreement.pdf" }],
    "recipients": [
      { "key": "maria", "name": "Maria Lopez", "email": "maria@bluefern.example" }
    ],
    "fields": [
      { "recipient": "maria", "type": "signature",
        "page": 3, "x": 72, "y": 640, "w": 180, "h": 36, "unit": "pt" },
      { "recipient": "maria", "type": "date",
        "page": 3, "x": 300, "y": 640, "w": 110, "h": 24, "unit": "pt" }
    ]
  }'

Response

{
  "id": "env_01JB7Q2M8X4K",
  "status": "sent",
  "test_mode": true,
  "title": "Merchant agreement – Blue Fern Café",
  "recipients": [
    { "id": "rcp_01JB7Q2M9A1T", "key": "maria", "status": "sent" }
  ],
  "billed": false,
  "links": {
    "audit": "/v1/envelopes/env_01JB7Q2M8X4K/audit",
    "final": "/v1/envelopes/env_01JB7Q2M8X4K/documents/final"
  }
}

A test key returns "test_mode": true and "billed": false. Switch to your live key and the same call sends a real, billed envelope.

How it works

Send

POST a PDF with recipients and field positions in points, pixels, percent or text anchors. Sealpost checks every field lands on the page before anything goes out.

Sign

Each signer gets one email link. They read, consent, sign and finish in the browser, on a phone or a desk, in English or Spanish. No account, no app.

Seal

When the last person signs, Sealpost stamps the fields, adds a certificate page, and seals the PDF with a key held in a hardware security module. You get envelope.sealed by webhook and download the final PDF and its audit JSON.

Three things you will not find elsewhere

You pay for what you send

$1 per envelope, metered as it happens, with a monthly cap you set yourself. Reminders, views, downloads, API reads and webhook deliveries are never charged. The usage page shows the same numbers we bill from.

See pricing

Nothing is behind a plan

There are no plans. Embedded signing, webhooks with a delivery log and replay, templates, bulk export and SMS authentication are on every account from the first day. The only thing that changes as you grow is the number on your invoice.

Agents can send it too

Sealpost ships an MCP server, so Claude, Cursor or your own agent can send a document and track it. Sending needs an explicit confirm: true, and every agent action is written to your audit log.

How agents use it

The record holds up

Sealed, not just signed. The final PDF carries a PAdES digital seal with a trusted timestamp. Any PDF reader can show whether a single byte changed since sealing.
The audit trail is data. Every event, from created to sealed, comes back as JSON with time, IP address, device and a hash chain you can verify yourself. No scraping a PDF page.
Stored so it cannot be quietly changed. Sealed documents sit in write-once storage, encrypted with a key that belongs to your account alone.
Built to the HIPAA standard. The same controls run for every account, whether you send merchant agreements or patient forms.

How it works in detail

Start in test mode today

Get a test key, send yourself a document, and see the sealed PDF before you spend a dollar.

Get a test key

E-signatures for developers.$1 per envelope you send.