StaySigned vs Signbee: Developer E-Signature APIs Compared (2026)

The Developer E-Signature Landscape in 2026

Integrating digital signatures into software applications used to mean accepting enterprise bloat. Developers building SaaS platforms, fintech tools, or internal ops tools were forced to navigate 50-page API manuals, set up OAuth 2.0 flows, drag signature boxes across web portals, and map absolute X/Y pixel coordinates just to request a signature on an agreement.

In 2026, the requirements have changed dramatically. Modern engineering teams are shipping automated workflows, serverless functions, and autonomous AI agents (built on Claude, Cursor, Windsurf, LangChain, or custom frameworks) that generate contracts on the fly. These systems don't have human operators sitting at screens dragging input boxes. They need a deterministic, single-endpoint API primitive that handles document compilation, signature field positioning, delivery, and cryptographically secure webhooks.

When developers evaluate alternatives like StaySigned and Signbee, the choice comes down to architectural philosophy. Is the e-signature API an extension of a legacy GUI document editor, or is it a clean, headless developer primitive? To understand which tool fits your stack, read our guide to the 10 best e-signature APIs for developers in 2026.

1. Endpoint Simplicity & API Architecture

The most immediate difference between StaySigned and Signbee is the engineering effort required to issue a single signature request.

StaySigned API Architecture: StaySigned follows a multi-step object pipeline typical of traditional document platforms. To dispatch a contract for signing via StaySigned, your application must typically execute a multi-step sequence:

1. Upload a source PDF file to a temporary storage container (POST /v1/documents).
2. Create a document instance bound to a pre-defined template ID or raw file reference.
3. Define recipient roles, field types, and absolute coordinate locations (X, Y, page number) or regex anchor tags.
4. Issue a dispatch request (POST /v1/documents/{id}/send) to initiate signature emails.
5. Poll the status endpoint or await asynchronous webhook callbacks to manage multi-state transitions (Draft → Sent → Completed).

This multi-step orchestration adds state management overhead to your backend microservices. If any step fails halfway through, your code must handle retries, orphan document cleanup, and state reconciliation.

Signbee Single-Endpoint Primitive: Signbee replaces multi-step pipelines with a single, idempotent API call to POST /api/v1/send. You pass the contract content (as clean Markdown text or a public PDF URL), the sender email, and recipient details in a single JSON payload. The API compiles the document, injects signature blocks automatically, dispatches notification emails, and returns a tracking confirmation immediately.

POST /api/v1/send
Content-Type: application/json
Authorization: Bearer sb_live_secret_key_12345

{
  "title": "Master Services Agreement",
  "markdown": "# Master Services Agreement\n\nThis agreement is made between Party A and Party B...\n\n[Signer: Jane Doe, jane@example.com]",
  "sender": { "name": "Acme Corp", "email": "contracts@acme.com" }
}

By consolidating document creation, field injection, and delivery into one HTTP POST request, Signbee eliminates state-machine complexity in your backend. For more context on why single-endpoint design matters, check out our analysis of DocuSign vs Signbee: 400 endpoints vs 1.

2. Pricing Breakdown: $0.50/Doc Parity vs True Pay-As-You-Go

Pricing predictability is a major friction point for developers evaluating e-signature APIs. Both StaySigned and Signbee highlight unit economics around $0.50 per document, but the financial terms behind that number differ significantly.

StaySigned Pricing Mechanics: StaySigned structures its pricing around tiered monthly plans and minimum volume commits. While their marketing highlights $0.50 per document rates at higher tiers, reaching that unit price requires locking into minimum monthly spending thresholds (e.g., $100–$250/month minimum commitments). If your app sends fewer documents during slow months, your effective cost per document spikes. Furthermore, StaySigned may bill separately for extra team seats, secondary API keys, or enterprise webhook features.

Signbee Transparent Pay-As-You-Go: Signbee offers true pay-as-you-go pricing with zero monthly minimums, zero seat taxes, and zero credit expiration.

• Free Tier: 5 real, legally binding signed documents per month forever. No credit card required, operating directly on the production engine.
• Pay-As-You-Go: Flat $0.50 per document for additional documents. Pay only for what you send.
• Zero Per-Seat Fees: Invite your entire engineering team, sales reps, or AI agent worker threads at no extra charge.

For a granular breakdown of how various platforms structure unit costs and minimum commitments, view our complete e-signature API pricing comparison for 2026.

3. Template Dependence vs Dynamic Markdown Flow

In traditional e-signature platforms like StaySigned, document templates are managed through a graphical user interface (GUI).

The Problem with GUI Templates: When a user or system needs to sign a contract, StaySigned retrieves a template PDF created in its web app and injects text values into pre-defined field coordinates. This approach works well for static forms, but fails when generating dynamic agreements. If a contract clause expands from 2 paragraphs to 5, text on subsequent pages shifts down while static signature boxes remain locked to absolute coordinates—resulting in signature boxes floating over body text or landing on empty pages.

Signbee's Native Markdown Engine: Signbee eliminates template dependencies by compiling standard Markdown directly into styled PDFs at generation time. Developers embed smart signature tags directly within the Markdown body text:

# Independent Contractor Agreement

## 1. Scope of Work
The contractor agrees to perform the following services: {{custom_scope_text}}

## 2. Execution & Signatures
In witness whereof, the parties have executed this Agreement as of {{current_date}}.

[Signer: Contractor Name, contractor@client.com]
[Signer: Client Representative, client@company.com]

Because signature tags live inline within the Markdown source, Signbee dynamically calculates layout bounds during compilation. Signature blocks, date lines, and audit footers auto-flow naturally at the end of the document text regardless of dynamic content length.

4. Webhook Security: HMAC-SHA256 Cryptographic Verification

When a signer completes a document, your backend application relies on webhooks to trigger downstream business logic—such as granting SaaS access, activating a subscription, or releasing funds. If an attacker spoofs webhook notifications, they can trick your system into executing actions without valid signatures.

StaySigned Webhook Handling: StaySigned typically provides standard webhook notifications using static secret headers or basic bearer tokens. While functional over HTTPS, static tokens offer weak defense against replay attacks or compromised endpoint secrets.

Signbee HMAC-SHA256 Cryptographic Verification: Signbee signs every outgoing HTTP webhook payload with an HMAC-SHA256 signature using your secret webhook key. Each webhook payload includes two critical security headers:

• X-Signbee-Signature: The hex-encoded HMAC-SHA256 hash calculated over timestamp + '.' + raw_json_body.
• X-Signbee-Timestamp: The UNIX timestamp when the event was dispatched.

This architecture allows your server to verify payload authenticity and reject stale or replayed webhook requests outside a 5-minute tolerance window.

5. AI Agent Discoverability (llms.txt & MCP Support)

As autonomous AI agents assume responsibility for executing business workflows—generating proposals, executing vendor NDAs, and filing compliance documents—API discoverability for machines is as critical as developer documentation for humans.

StaySigned Machine Readiness: StaySigned is designed for human developers reading OpenAPI docs in browser tabs. It offers no machine-readable agent manifests, no native Model Context Protocol (MCP) server integration, and no standardized LLM prompt primitives. To connect StaySigned to an agent framework, developers must write custom wrapper functions and handle multi-step state polling manually.

Signbee AI-First Architecture: Signbee is engineered natively for the agentic stack:

• Native MCP Server: Signbee provides an official Model Context Protocol (MCP) server. AI agents running in Claude Desktop, Cursor, Windsurf, or custom agent runtimes can discover and execute e-signature tools directly.
• llms.txt Standard: Signbee hosts a standardized llms.txt file at the domain root, enabling LLMs to auto-discover API routes, request schemas, and sample payloads without human intervention.
• Single Tool Call: Because Signbee requires only one API endpoint to send a document, an AI agent can issue a complete contract request in a single LLM tool call.

6. Detailed Side-by-Side Features Table

The following matrix compares StaySigned API vs Signbee API across 10 core developer dimensions:

7. Code Comparison: cURL & Node.js Implementation

Let's examine how implementation code looks in practice when dispatching an agreement and handling webhooks.

Sending a Document via cURL

With Signbee, you can send an NDA or contract directly from your terminal or server script using a single cURL command:

curl -X POST https://api.signb.ee/v1/send \
  -H "Authorization: Bearer sb_live_secret_key_998877" \
  -H "Content-Type: application/json" \
  -d '{
    "title": "Non-Disclosure Agreement",
    "markdown": "# Mutual Non-Disclosure Agreement\n\nThis agreement governs confidential information shared between the parties...\n\n[Signer: Founder, founder@startup.com]",
    "sender": {
      "name": "Signbee Inc",
      "email": "hello@signb.ee"
    }
  }'

Node.js Implementation: Dispatch & Secure Webhook Handler

Here is a full Node.js / Express example demonstrating how to send a contract and verify Signbee HMAC-SHA256 webhook signatures securely in backend code:

import express from 'express';
import crypto from 'crypto';

const app = express();
app.use(express.json({
  verify: (req, res, buf) => {
    req.rawBody = buf; // Preserve raw body for HMAC verification
  }
}));

const SIGNBEE_API_KEY = process.env.SIGNBEE_API_KEY;
const WEBHOOK_SECRET = process.env.SIGNBEE_WEBHOOK_SECRET;

// 1. Dispatch Document to Signbee API
async function sendDocument() {
  const response = await fetch('https://api.signb.ee/v1/send', {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${SIGNBEE_API_KEY}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      title: 'Consulting Contract 2026',
      markdown: `
# Consulting Services Agreement

This Agreement is entered into as of July 17, 2026.

## Services & Payment
Consultant shall provide software engineering services at a rate of $150/hr.

[Signer: Alex Rivera, alex@example.com]
      `,
      sender: { name: 'Client Co', email: 'ops@clientco.com' }
    }),
  });

  const data = await response.json();
  console.log('Document sent successfully:', data.id);
}

// 2. Secure HMAC-SHA256 Webhook Verification Endpoint
app.post('/api/webhooks/signbee', (req, res) => {
  const signatureHeader = req.headers['x-signbee-signature'];
  const timestampHeader = req.headers['x-signbee-timestamp'];

  if (!signatureHeader || !timestampHeader) {
    return res.status(400).send('Missing webhook security headers');
  }

  // Prevent replay attacks (5-minute window tolerance)
  const now = Math.floor(Date.now() / 1000);
  if (Math.abs(now - parseInt(timestampHeader, 10)) > 300) {
    return res.status(401).send('Webhook timestamp outside valid tolerance window');
  }

  // Compute HMAC-SHA256 over timestamp + raw payload
  const payloadToSign = `${timestampHeader}.${req.rawBody.toString('utf8')}`;
  const computedSignature = crypto
    .createHmac('sha256', WEBHOOK_SECRET)
    .update(payloadToSign)
    .digest('hex');

  if (crypto.timingSafeEqual(Buffer.from(signatureHeader), Buffer.from(computedSignature))) {
    const event = req.body;
    console.log(`Verified Webhook Event ${event.type} for document ${event.document_id}`);
    return res.status(200).json({ received: true });
  } else {
    return res.status(403).send('Invalid HMAC signature');
  }
});

app.listen(3000, () => console.log('Server running on port 3000'));

Which E-Signature API Should You Choose?

Both StaySigned and Signbee solve electronic signature requirements, but they cater to distinct operational workflows:

Choose StaySigned if:

• Your organization relies on a web-based GUI template builder where non-technical ops staff create static PDF templates.
• Your document volume is steady, predictably hitting mid-tier monthly minimum allocations.
• You prefer traditional REST API structures with multi-step draft-to-send pipelines.

Choose Signbee if:

• You are a software engineer, startup, or product team looking for a clean, single-endpoint (POST /api/v1/send) signing primitive.
• You want transparent $0.50/doc pay-as-you-go pricing with zero monthly minimums, zero seat taxes, and 5 free docs per month forever.
• You generate dynamic contracts in Markdown or pass PDF URLs programmatically without managing GUI templates or coordinate mapping scripts.
• You require enterprise-grade HMAC-SHA256 webhook cryptographic verification for security compliance.
• You are building AI-agentic workflows and need native Model Context Protocol (MCP) server support and llms.txt discoverability.

Frequently Asked Questions