Electronic Signature API for Developers (2026)

# Electronic Signature API for Developers (2026)

TL;DR

If you need an electronic signature API in 2026, four options are worth real consideration: SignQuick (no free tier, API on the Business plan, EU-hosted, eIDAS audit trail on every plan), Dropbox Sign (3 docs/month per user, but API is trial-only after 30 days), SignWell (3 docs/month, US-hosted), and Documenso (open-source, free if you self-host).

"Free" means different things. SignWell gives you production API keys forever with a monthly document cap. SignQuick has no free tier: API access comes with the Business plan. Dropbox Sign requires a paid plan to keep API access after the trial. Documenso is free only if you run the infrastructure yourself.

Most teams graduate off the free tier around 20–30 signature requests per month — at which point Starter plans (€10–€20/mo) become the obvious next step. White-label (your logo on the signing page) is a separate upgrade across all four providers.

What an e-signature API actually does

A hosted e-signature dashboard is for humans clicking "send for signature." An API is for code. The typical surface area:

• Programmatic document upload + send — POST a PDF and a list of signers, get back a signing URL per recipient.
• Embedded signing — render the signing page inside your own app via an iframe or redirect, instead of sending the recipient to the vendor's domain.
• Webhooks — receive `signed`, `declined`, `viewed`, and `expired` events so your backend can update order state without polling.
• Template + field placement — define signature, date, and text fields by coordinate or by anchor text ("Sign here →").
• Audit trail retrieval — fetch the signed PDF plus a separate audit-trail PDF with IPs, timestamps, and document hash.

If you only need to send a contract once a week, use the dashboard. If signing is part of an onboarding, checkout, or HR flow, you want the API.

E-signature API comparison (2026)

Two non-obvious notes. First, Dropbox Sign (formerly HelloSign, acquired by Dropbox in 2019 and rebranded August 2022) does not include API calls on its free user plan — you need a paid API plan once the 30-day trial ends. Second, Adobe Acrobat Sign no longer has a meaningful free API tier; the standalone Adobe Sign brand was folded into Acrobat Sign in 2022 and pricing starts around $14.99/user/mo with no perpetual free API.

Quickstart: send your first signing request in 5 curl commands

Replace sq__YOUR_API_KEY with the key from your SignQuick developer dashboard.

1. Upload a document

curl -X POST https://api.signquick.app/v1/documents \
  -H "Authorization: Bearer sq__YOUR_API_KEY" \
  -F "[email protected]" \
  -F "name=Service Agreement"

Response includes { "id": "doc_abc123" }.

2. Add a signer field by anchor text

curl -X POST https://api.signquick.app/v1/documents/doc_abc123/fields \
  -H "Authorization: Bearer sq__YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"type":"signature","anchor":"Signature:","signer":"[email protected]"}'

3. Create the signing request

curl -X POST https://api.signquick.app/v1/signing-requests \
  -H "Authorization: Bearer sq__YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"document_id":"doc_abc123","signers":[{"email":"[email protected]","name":"Jane Client"}]}'

4. Register a webhook endpoint

curl -X POST https://api.signquick.app/v1/webhooks \
  -H "Authorization: Bearer sq__YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"url":"https://yourapp.com/hooks/signquick","events":["signed","declined","expired"]}'

5. Download the signed PDF

curl -X GET https://api.signquick.app/v1/signing-requests/req_xyz789/signed.pdf \
  -H "Authorization: Bearer sq__YOUR_API_KEY" \
  --output signed.pdf

That's the full loop: upload, place field, send, get notified, download. The eIDAS audit-trail PDF is available at the same endpoint with .audit-trail instead of .signed.

Webhook events worth subscribing to

Four events cover 95% of integrations. Here's a minimal Express handler:

app.post('/hooks/signquick', (req, res) => {
  const { event, signing_request_id, signer_email, timestamp } = req.body;

  switch (event) {
    case 'viewed':
      // Signer opened the document — useful for nudge campaigns
      break;
    case 'signed':
      // All signers complete — trigger downstream (provision account, etc.)
      break;
    case 'declined':
      // Signer rejected — flag for sales follow-up
      break;
    case 'expired':
      // Hit the expiration date without signing
      break;
  }

  res.status(200).send('ok');
});

Always verify the X-SignQuick-Signature HMAC header against your webhook secret before trusting the payload. Skip this step and an attacker who guesses your endpoint URL can fake completion events.

When to move up to a bigger plan

A free tier of three documents per month is enough to prototype, run a demo for your team, or handle one or two contracts in a side project. The signs you've outgrown it:

• You're hitting the cap before the 20th of the month.
• You need more than three signers per request.
• You want your logo on the signing page (white-label).
• You need longer document retention than a free tier gives.
• A customer asks for SSO or SCIM.

At that point, SignQuick Business (€19/mo, unlimited documents, API included) is the typical landing spot once signing is core to your product flow. For lighter use without the API, Pro is €9/mo (25 docs) or you can pay €2.99 per document. Agencies reselling to clients should look at the White-Label tiers (€150/mo Starter, €300/mo Pro) — full breakdown on the pricing page.

FAQ

Is there a truly free electronic signature API?

Yes, though not with SignQuick. Documenso is free if you self-host. Dropbox Sign and SignWell offer limited free tiers but Dropbox Sign restricts API access to a 30-day trial. SignQuick has no free tier: full API and webhook access comes with the Business plan, and the 14-day white-label trial lets you evaluate it.

How many documents can I send during the trial?

SignQuick's API is included on the Business plan, and free to evaluate during the 14-day white-label trial. Beyond that, Pro is €9/mo (25 docs) and Business is €19/mo (unlimited).

Can I white-label the signing page through the API?

The signing page branding is controlled by your plan, not the API call. White-label (custom logo, color, company name) requires the White-Label Starter (€150/mo) or Pro (€300/mo). The API itself is identical across tiers.

Does the trial include an eIDAS-compliant audit trail?

Yes. Every signing request on SignQuick generates an eIDAS-compliant audit trail with timestamps, signer IP, and document hash, attached to the final signed PDF.

Which SDK languages are officially supported?

SignQuick exposes a REST API usable from any language. An official SDK ships for JavaScript/TypeScript (Node), a Python SDK is coming soon, and an MCP server is available. Dropbox Sign covers Node, Python, Ruby, PHP, Java, and C#. SignWell ships Node and Python. Documenso is TypeScript-only.