Built for AI Agents

SignSimple's free e-signature workflow is fully programmable. Whether you're an agent, an assistant, or a developer: send a PDF, get it legally signed, and download the certified result — through MCP or plain REST.

1. Get an API key

Create a free account, then mint a key on your profile page. Keys look like ss_live_..., are shown once, and are stored only as a hash. Send the key with every request as X-Api-Key or Authorization: Bearer ss_live_....

2. Connect via MCP (recommended for agents)

A hosted Model Context Protocol server runs at https://signsimple.app/mcp (Streamable HTTP). It exposes four tools: send_for_signature, get_document_status, list_documents, and list_templates. Discovery works without a key; account tools need one. Example client configuration:

{
  "mcpServers": {
    "signsimple": {
      "type": "http",
      "url": "https://signsimple.app/mcp",
      "headers": {
        "Authorization": "Bearer ss_live_YOUR_KEY_HERE"
      }
    }
  }
}

In Claude Code: claude mcp add --transport http signsimple https://signsimple.app/mcp --header "Authorization: Bearer ss_live_..."

3. Or call the REST API directly

Full OpenAPI 3.1 spec at /openapi.json. Send a document:

curl https://us-central1-signsimple-app.cloudfunctions.net/agentSend \
  -H "Content-Type: application/json" \
  -H "X-Api-Key: ss_live_YOUR_KEY_HERE" \
  -d '{
    "documentUrl": "https://signsimple.app/templates/nda.pdf",
    "documentName": "Mutual NDA.pdf",
    "recipients": [
      { "name": "Jordan Lee", "email": "jordan@example.com" }
    ],
    "expiresInDays": 14
  }'

The response includes the envelopeId and each recipient's signing link. Recipients are emailed automatically; signature and date fields are placed on the last page unless you pass a fields array with exact geometry. Then poll:

curl https://us-central1-signsimple-app.cloudfunctions.net/agentStatus \
  -H "Content-Type: application/json" \
  -H "X-Api-Key: ss_live_YOUR_KEY_HERE" \
  -d '{ "envelopeId": "env_1786..." }'

When every recipient has signed, the status response carries signedPdfUrl: the final PDF with every signature and a certificate page listing each signer, timestamps, and the SHA-256 hash of the original document.

Discovery endpoints

/llms.txt — plain-language overview for LLMs
/openapi.json — OpenAPI 3.1 spec
/.well-known/agent-card.json — agent card (capabilities + interfaces)
/.well-known/mcp.json — MCP server discovery
https://signsimple.app/mcp — the MCP endpoint itself

Free templates, sendable by URL

Every template in the free template gallery (NDA, lease, contractor agreement, liability waiver, bill of sale, promissory note) has a stable PDF URL you can pass straight to send_for_signature as documentUrl.

Pricing and limits

The API is free, like the rest of SignSimple: no per-document fees and no monthly caps. PDFs up to 15 MB, up to 10 recipients per send, up to 5 active API keys per account. Signed documents are legally binding under the U.S. ESIGN Act.