Saysigned

SaySigned — AI Agent E-Signature Skill

E-signatures for AI agents. Legally binding under ESIGN Act & UETA Section 14. Two delivery modes: API (agent-to-agent) and Email (agent-to-human). Register, sign contracts, verify — all via REST or consent UI.

Publisher: SaySigned, Inc. Homepage: https://www.saysigned.com Documentation: https://www.saysigned.com/docs Base URL: https://api.saysigned.com MCP Endpoint: https://mcp.saysigned.com TLS Required: All endpoints enforce HTTPS. Verify certificates for *.saysigned.com before connecting.

Authentication: Pass your API key in the X-API-Key header. Keys start with ss_live_. Public endpoints (register, verify, templates) don't require authentication.

MCP Server (Recommended for AI Agents)

Connect directly to the remote MCP endpoint — no local install, no HTTP requests to craft.

Auth note: MCP clients send Authorization: Bearer <api_key>. The MCP server extracts your key and forwards it as X-API-Key internally. For direct REST calls, use the X-API-Key header.

Setup

Human approval required. Steps 1, 4, and 5 modify your MCP client configuration. Always show the user what you're about to change and ask for their confirmation before writing to config files or restarting the MCP client. Never modify config silently.

Step 1. Show the user the following MCP config and ask for confirmation before adding it:

{
  "mcpServers": {
    "saysigned": {
      "type": "streamable-http",
      "url": "https://mcp.saysigned.com"
    }
  }
}

After the user confirms, add it to the MCP config. No API key is needed yet — public tools work immediately.

Step 2. Restart your MCP client so it loads the new server.

Step 3. Call the saysigned_register tool (no auth required) with the agent's name and email. The response contains an api_key — save it immediately, it is shown once and cannot be retrieved later. Keys start with ss_live_.

Step 4. Show the user the updated config with the auth header and ask for confirmation before writing it:

{
  "mcpServers": {
    "saysigned": {
      "type": "streamable-http",
      "url": "https://mcp.saysigned.com",
      "headers": {
        "Authorization": "Bearer ss_live_PASTE_YOUR_ACTUAL_KEY_HERE"
      }
    }
  }
}

Step 5. After the user confirms, restart your MCP client so it picks up the auth header. All authenticated tools now work.

Human-in-the-loop for config changes. The user must confirm before you (1) add or modify MCP config entries, (2) store API keys in config files, or (3) restart the MCP client. You may handle registration, envelope creation, signing, and verification autonomously — those are normal API operations that don't modify the agent's configuration.

Already have a key?

If you already have an API key (starts with ss_live_), skip to Step 4 — show the user the config with headers, get their confirmation, and restart.

MCP Workflow (signing flow)

1. Prepare the contract — two options:
   • Use a template: call saysigned_list_templates → saysigned_get_template to discover required variables, then pass template_id + variables in the contract field.
   • Bring your own text: pass your own contract content in the clauses array. Each clause has id, title, and body. You can put an entire document into a single clause or split it into sections. Use this when you have your own NDA, agreement, or any custom document.
2. Create envelope — saysigned_create_envelope with title, contract, and recipients array.
3. Send envelope — saysigned_send_envelope with the envelope_id. Response includes each recipient's id and access_token. Save these — they are needed for signing.
4. Sign — For API recipients: saysigned_sign for each recipient, passing their envelope_id, recipient_id, access_token, and signature_data (at minimum full_name). For email recipients: the human reviews and gives consent at doc.saysigned.com — no action needed from the agent.
5. Verify — saysigned_verify with the envelope_id. No auth needed.

Critical Notes for AI Agents

• You don't have to use a template. If you have your own contract text (an NDA, agreement, policy — any document), pass it directly via clauses. Templates are a convenience, not a requirement.
• Always call saysigned_get_template before creating an envelope with a template. The required variables differ per template and the API will reject unknown or missing variables.
• saysigned_send_envelope returns access tokens. You must capture and use these tokens for signing. They are 128-character hex strings.
• Signing does not use your API key. The saysigned_sign and saysigned_decline tools authenticate via the access_token parameter, not the API key header.
• The envelope auto-completes when the last recipient signs. You don't need to call a separate "complete" endpoint.
• Auth header is forwarded automatically. Authenticated tools (create_envelope, send_envelope, get_envelope, get_profile, etc.) use the API key from your MCP client's Authorization header. Public tools (register, verify, list_templates, get_template) work without it.
• delivery_method: "email" sends a signing link to a real human. The human reviews the contract at doc.saysigned.com and gives consent via browser. Email recipients do NOT get an access_token in the send response — they authenticate via a URL token in their email link. Use delivery_method: "api" (default) for agent-to-agent signing.
• Poll or use webhooks for email recipients. Since humans sign asynchronously, use saysigned_get_envelope to poll for status changes or configure a webhook_url to receive recipient.viewed and recipient.signed events.

All 14 MCP Tools

Complete End-to-End Example

This is a full working flow: register, create an NDA, send it, both parties sign, then verify. Every response shown is from the real production API.

Step 1 — Register (no auth needed)

curl -s -X POST https://api.saysigned.com/agents/register \
  -H "Content-Type: application/json" \
  -d '{"name": "My AI Agent", "email": "agent@example.com"}'

{
  "agent_id": "7773b4af-44d1-44fc-8db7-05d9bc95b541",
  "api_key": "ss_live_203bff0e53ba167462aa2cdcbd8e189e2909d37cf76c31da675cb1dba7dc0026",
  "plan": "free",
  "free_envelopes_remaining": 5
}

Save the api_key — it is shown once and cannot be retrieved later.

Step 2 — Create an envelope

Use the api_key from step 1 in the X-API-Key header. Use template_id for standard contracts or provide custom clauses.

curl -s -X POST https://api.saysigned.com/envelopes \
  -H "Content-Type: application/json" \
  -H "X-API-Key: ss_live_203bff0e53ba167462aa2cdcbd8e189e2909d37cf76c31da675cb1dba7dc0026" \
  -d '{
    "title": "Mutual NDA — Acme & Beta",
    "contract": {
      "template_id": "nda_mutual_v1",
      "variables": {
        "disclosing_party_name": "Acme Corp",
        "receiving_party_name": "Beta Inc",
        "effective_date": "2026-02-09",
        "purpose": "Evaluating a potential partnership",
        "governing_law_state": "California"
      }
    },
    "recipients": [
      {"name": "Alice", "email": "alice@acme.com", "role": "signer"},
      {"name": "Bob", "email": "bob@beta.com", "role": "signer"}
    ]
  }'

{
  "id": "2c272d15-cd4b-4c0d-96c0-bd7438b66699",
  "status": "draft",
  "title": "Mutual NDA — Acme & Beta",
  "recipients": [
    {"id": "62f73ba5-05a0-4223-8f55-e880047a7b3e", "name": "Alice", "status": "pending"},
    {"id": "cc0aeb32-eb9d-420d-ab93-1d42400f85b9", "name": "Bob", "status": "pending"}
  ]
}

Save the envelope id and each recipient's id.

Step 3 — Send the envelope

This consumes 1 envelope from your quota (free tier) or reports 1 metered event (paid plan). Recipients get access_token values — these are how they authenticate when signing.

curl -s -X POST https://api.saysigned.com/envelopes/2c272d15-cd4b-4c0d-96c0-bd7438b66699/send \
  -H "X-API-Key: ss_live_203bff0e53ba167462aa2cdcbd8e189e2909d37cf76c31da675cb1dba7dc0026"

{
  "id": "2c272d15-cd4b-4c0d-96c0-bd7438b66699",
  "status": "sent",
  "recipients": [
    {"id": "62f73ba5-05a0-4223-8f55-e880047a7b3e", "name": "Alice", "status": "sent", "access_token": "600b9b4297b2921396a1db138a80801c7dfb5101..."},
    {"id": "cc0aeb32-eb9d-420d-ab93-1d42400f85b9", "name": "Bob", "status": "sent", "access_token": "952340a770b96740e2696c306ad490b28556952e..."}
  ]
}

Save each recipient's access_token. Distribute tokens to the respective signers.

Step 4 — Recipients sign

Each recipient signs using their access_token via the X-Access-Token header (recommended) or ?access_token= query parameter. No API key needed — the token is the auth.

# Alice signs
curl -s -X POST "https://api.saysigned.com/envelopes/2c272d15-cd4b-4c0d-96c0-bd7438b66699/recipients/62f73ba5-05a0-4223-8f55-e880047a7b3e/sign" \
  -H "Content-Type: application/json" \
  -H "X-Access-Token: 600b9b4297b2921396a1db138a80801c7dfb5101..." \
  -d '{"signature_data": {"full_name": "Alice Chen", "title": "CEO"}}'

{
  "signed": true,
  "recipient_id": "62f73ba5-05a0-4223-8f55-e880047a7b3e",
  "envelope_id": "2c272d15-cd4b-4c0d-96c0-bd7438b66699",
  "signed_at": "2026-02-09T04:09:24.111Z"
}

# Bob signs (last signer → envelope automatically completes with RFC 3161 timestamp)
curl -s -X POST "https://api.saysigned.com/envelopes/2c272d15-cd4b-4c0d-96c0-bd7438b66699/recipients/cc0aeb32-eb9d-420d-ab93-1d42400f85b9/sign" \
  -H "Content-Type: application/json" \
  -H "X-Access-Token: 952340a770b96740e2696c306ad490b28556952e..." \
  -d '{"signature_data": {"full_name": "Bob Smith", "title": "CTO"}}'

{
  "signed": true,
  "recipient_id": "cc0aeb32-eb9d-420d-ab93-1d42400f85b9",
  "envelope_id": "2c272d15-cd4b-4c0d-96c0-bd7438b66699",
  "signed_at": "2026-02-09T04:09:25.190Z"
}

Step 5 — Verify (public, no auth needed)

curl -s -X POST https://api.saysigned.com/verify \
  -H "Content-Type: application/json" \
  -d '{"envelope_id": "2c272d15-cd4b-4c0d-96c0-bd7438b66699"}'

{
  "envelope_id": "2c272d15-cd4b-4c0d-96c0-bd7438b66699",
  "status": "completed",
  "chain_verification": {"valid": true, "entries_checked": 5},
  "timestamp_verification": {
    "valid": true,
    "gen_time": "2026-02-09T04:09:25+00:00",
    "tsa_name": "DigiCert SHA256 RSA4096 Timestamp Responder 2025 1"
  },
  "recipients": [
    {"name": "Alice", "email": "alice@acme.com", "role": "signer", "status": "signed", "signed_at": "2026-02-09T04:09:24.111Z"},
    {"name": "Bob", "email": "bob@beta.com", "role": "signer", "status": "signed", "signed_at": "2026-02-09T04:09:25.190Z"}
  ],
  "completed_at": "2026-02-09T04:09:25.039Z"
}

Bring Your Own Contract

You don't need a template. If you have your own document text — an NDA your user provided, a custom agreement, any markdown or plain text — pass it directly via clauses. Each clause needs an id, title, and body.

Single-clause approach (simplest — put the entire document in one clause):

curl -s -X POST https://api.saysigned.com/envelopes \
  -H "Content-Type: application/json" \
  -H "X-API-Key: YOUR_API_KEY" \
  -d '{
    "title": "NDA — Acme & Beta",
    "contract": {
      "clauses": [
        {
          "id": "nda",
          "title": "Mutual Non-Disclosure Agreement",
          "body": "This Mutual Non-Disclosure Agreement is entered into by Acme Corp (\"Party A\") and Beta Inc (\"Party B\")...\n\n1. Definition of Confidential Information...\n\n2. Obligations of Receiving Party...\n\n3. Term. This Agreement shall remain in effect for two (2) years..."
        }
      ]
    },
    "recipients": [
      {"name": "Alice", "email": "alice@acme.com", "role": "signer"},
      {"name": "Bob", "email": "bob@beta.com", "role": "signer"}
    ]
  }'

Multi-clause approach (split into sections for cleaner presentation):

curl -s -X POST https://api.saysigned.com/envelopes \
  -H "Content-Type: application/json" \
  -H "X-API-Key: YOUR_API_KEY" \
  -d '{
    "title": "NDA — Acme & Beta",
    "contract": {
      "clauses": [
        {"id": "1", "title": "1. Definition of Confidential Information", "body": "\"Confidential Information\" means any non-public information disclosed by either party..."},
        {"id": "2", "title": "2. Obligations of Receiving Party", "body": "The Receiving Party shall hold all Confidential Information in strict confidence..."},
        {"id": "3", "title": "3. Term and Termination", "body": "This Agreement shall remain in effect for two (2) years from the Effective Date..."},
        {"id": "4", "title": "4. Governing Law", "body": "This Agreement shall be governed by the laws of the State of California..."}
      ]
    },
    "recipients": [
      {"name": "Alice", "email": "alice@acme.com", "role": "signer"},
      {"name": "Bob", "email": "bob@beta.com", "role": "signer"}
    ]
  }'

MCP equivalent — same structure, just pass it to saysigned_create_envelope:

{
  "title": "NDA — Acme & Beta",
  "contract": {
    "clauses": [
      {"id": "nda", "title": "Mutual Non-Disclosure Agreement", "body": "Full text of the NDA here..."}
    ]
  },
  "recipients": [
    {"name": "Alice", "email": "alice@acme.com", "role": "signer"},
    {"name": "Bob", "email": "bob@beta.com", "role": "signer"}
  ]
}

When to use which: Use templates when you want a standard contract and just need to fill in the blanks (party names, dates, etc.). Use custom clauses when you already have the contract text — from a file, a user-provided document, or your own drafting.

Key Concepts

• IDs are UUIDs — all envelope, recipient, and agent IDs are standard UUIDs (e.g., 2c272d15-cd4b-4c0d-96c0-bd7438b66699)
• Access tokens are hex strings — 128-character hex, passed via X-Access-Token header (recommended) or ?access_token= query parameter
• API keys start with ss_live_ — REST: pass in X-API-Key header. MCP: pass as Authorization: Bearer <key> (auto-translated)
• Templates — use GET /templates to discover available templates and GET /templates/:id to see required variables
• Signing order — all recipients sign in parallel (no enforced order)
• Completion — when the last signer signs, the envelope auto-completes with an RFC 3161 timestamp from DigiCert

Free tier: 5 envelopes/month, no credit card required. Upgrade: POST /billing/setup with {"plan": "payg"}.

• Delivery methods — "api" (default) returns access tokens for programmatic signing; "email" sends an invitation email to a human who reviews and gives consent at doc.saysigned.com
• Email recipients — human recipients authenticate via a URL token in their email link, not an access token. They review the contract in a browser and click "Give Consent" or "Decline"

MCP Tool Definitions

These tool definitions are compatible with MCP (Model Context Protocol) runtimes. Each tool maps to a REST API endpoint.

saysigned_register

Create an agent account and get your API key.

{
  "name": "saysigned_register",
  "description": "Register a new AI agent account on SaySigned. Returns an API key (shown once — save it). Free tier: 5 envelopes/month.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "name": { "type": "string", "description": "Agent or organization name" },
      "email": { "type": "string", "format": "email", "description": "Contact email (must be unique)" },
      "company_name": { "type": "string", "description": "Company name (optional)" },
      "webhook_url": { "type": "string", "format": "uri", "description": "URL to receive webhook notifications (optional)" }
    },
    "required": ["name", "email"]
  }
}

REST: POST /agents/register — no auth required.

saysigned_create_envelope

Create a draft envelope with a contract and recipients.

{
  "name": "saysigned_create_envelope",
  "description": "Create a draft envelope with contract content and recipients. Two ways to provide a contract: (1) Use template_id + variables for standard contracts (call saysigned_get_template first), or (2) provide your own contract text via the clauses array — each clause has an id, title, and body. You can put an entire document into a single clause or split it into sections. Use option 2 when you have your own NDA, agreement, or any custom document text. Set delivery_method: 'email' on a recipient to send them a consent link via email instead of returning an access token. Does not send — call saysigned_send_envelope to dispatch.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "title": { "type": "string", "description": "Envelope title" },
      "description": { "type": "string", "description": "Brief description" },
      "contract": {
        "type": "object",
        "description": "Contract content. Use template_id + variables for templates, or provide raw clauses.",
        "properties": {
          "template_id": { "type": "string", "description": "Template ID (e.g., 'nda_mutual_v1', 'service_agreement_v1')" },
          "variables": { "type": "object", "description": "Template variables (see GET /templates/:id for schema)" },
          "clauses": {
            "type": "array",
            "description": "Custom clauses (when not using a template)",
            "items": {
              "type": "object",
              "properties": {
                "id": { "type": "string" },
                "title": { "type": "string" },
                "body": { "type": "string" }
              },
              "required": ["id", "title", "body"]
            }
          },
          "signature_block": {
            "type": "object",
            "description": "Custom signature block (when not using a template)"
          }
        }
      },
      "recipients": {
        "type": "array",
        "items": {
          "type": "object",
          "properties": {
            "name": { "type": "string" },
            "email": { "type": "string", "format": "email" },
            "role": { "type": "string", "enum": ["signer", "cc", "approver", "witness"], "default": "signer" },
            "delivery_method": { "type": "string", "enum": ["api", "email"], "default": "api", "description": "'api' (default) for AI agent signing, 'email' to send a consent link to a human" }
          },
          "required": ["name", "email"]
        }
      },
      "expires_at": { "type": "string", "format": "date-time", "description": "Expiration date (optional)" },
      "metadata": { "type": "object", "description": "Custom key-value metadata (optional)" }
    },
    "required": ["title", "contract", "recipients"]
  }
}

REST: POST /envelopes — requires X-API-Key header.

Example — Custom contract (no template):

curl -s -X POST https://api.saysigned.com/envelopes \
  -H "Content-Type: application/json" \
  -H "X-API-Key: YOUR_API_KEY" \
  -d '{"title": "Data Processing Addendum", "contract": {"clauses": [{"id": "scope", "title": "1. Scope", "body": "This addendum governs the processing of personal data..."}], "signature_block": {"preamble": "Agreed and accepted:", "signers": [{"role": "Data Controller", "fields": ["signature", "printed_name", "date"]}]}}, "recipients": [{"name": "Controller Corp", "email": "legal@controller.com", "role": "signer"}]}'

saysigned_send_envelope

Send a draft envelope for signing. Consumes 1 envelope from your quota.

{
  "name": "saysigned_send_envelope",
  "description": "Send a draft envelope for signing. For API recipients, generates access tokens. For email recipients, sends an invitation email with a consent link to doc.saysigned.com (no access_token in response). Consumes 1 envelope (free tier) or reports 1 metered event (paid). Returns 402 if free tier exhausted.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "envelope_id": { "type": "string", "format": "uuid", "description": "ID of the draft envelope to send" }
    },
    "required": ["envelope_id"]
  }
}

REST: POST /envelopes/:id/send — requires X-API-Key header.

402 response (free tier exhausted):

{"error": "Free tier envelope limit exhausted. Upgrade to a paid plan."}

saysigned_sign

Sign an envelope as a recipient.

{
  "name": "saysigned_sign",
  "description": "Sign an envelope as a recipient. Provide the access_token from the send response as a query parameter. No API key needed — the token is the auth. Records IP, user-agent, and timestamp in the audit trail.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "envelope_id": { "type": "string", "format": "uuid" },
      "recipient_id": { "type": "string", "format": "uuid" },
      "access_token": { "type": "string", "description": "128-char hex token from the send response" },
      "signature_data": {
        "type": "object",
        "description": "Signature metadata",
        "properties": {
          "full_name": { "type": "string" },
          "title": { "type": "string" },
          "company": { "type": "string" }
        },
        "required": ["full_name"]
      }
    },
    "required": ["envelope_id", "recipient_id", "access_token", "signature_data"]
  }
}

REST: POST /envelopes/:id/recipients/:rid/sign with X-Access-Token: TOKEN header (recommended) or ?access_token=TOKEN query parameter. No API key needed.

saysigned_decline

Decline to sign an envelope.

{
  "name": "saysigned_decline",
  "description": "Decline to sign an envelope as a recipient. Optionally provide a reason.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "envelope_id": { "type": "string", "format": "uuid" },
      "recipient_id": { "type": "string", "format": "uuid" },
      "access_token": { "type": "string" },
      "reason": { "type": "string", "description": "Reason for declining (optional)" }
    },
    "required": ["envelope_id", "recipient_id", "access_token"]
  }
}

REST: POST /envelopes/:id/recipients/:rid/decline with X-Access-Token: TOKEN header (recommended) or ?access_token=TOKEN query parameter. No API key needed.

saysigned_get_envelope

Get envelope details and recipient status.

{
  "name": "saysigned_get_envelope",
  "description": "Get full details of an envelope including status, contract content, and recipient statuses.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "envelope_id": { "type": "string", "format": "uuid" }
    },
    "required": ["envelope_id"]
  }
}

REST: GET /envelopes/:id — requires X-API-Key header.

saysigned_void_envelope

Void (cancel) an envelope.

{
  "name": "saysigned_void_envelope",
  "description": "Void an envelope that has been sent but not yet completed. Cannot void completed envelopes.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "envelope_id": { "type": "string", "format": "uuid" },
      "reason": { "type": "string", "description": "Reason for voiding" }
    },
    "required": ["envelope_id"]
  }
}

REST: POST /envelopes/:id/void — requires X-API-Key header.

saysigned_verify

Cryptographically verify an envelope. Public — no authentication required.

{
  "name": "saysigned_verify",
  "description": "Verify the cryptographic integrity of an envelope. Checks the hash chain audit trail and RFC 3161 timestamp. Public endpoint — no API key needed.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "envelope_id": { "type": "string", "format": "uuid" }
    },
    "required": ["envelope_id"]
  }
}

REST: POST /verify

See the end-to-end example above for the real response format.

saysigned_get_audit_trail

Get the full hash-chain audit trail for an envelope.

{
  "name": "saysigned_get_audit_trail",
  "description": "Get the complete cryptographic audit trail for an envelope, including hash chain verification status.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "envelope_id": { "type": "string", "format": "uuid" }
    },
    "required": ["envelope_id"]
  }
}

REST: GET /envelopes/:id/audit-trail — requires X-API-Key header.

saysigned_get_profile

Get your agent profile and current usage.

{
  "name": "saysigned_get_profile",
  "description": "Get your agent profile, plan details, and current usage statistics.",
  "inputSchema": { "type": "object", "properties": {} }
}

REST: GET /agents/me — requires X-API-Key header.

saysigned_billing_setup

Upgrade from free tier to a paid plan. IMPORTANT: Always show the returned checkout_url to the human user so they can complete payment in their browser. Never silently consume the URL.

{
  "name": "saysigned_billing_setup",
  "description": "Upgrade to a paid plan. Creates a Stripe customer and returns a checkout URL. IMPORTANT: Always show the checkout_url to the human user so they can complete payment in their browser.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "plan": {
        "type": "string",
        "enum": ["payg", "commit_500", "commit_2000"],
        "description": "Plan to upgrade to. payg = $0.65/env, commit_500 (Pro) = $225/mo for 500 env, commit_2000 (Business) = $600/mo for 2000 env."
      }
    },
    "required": ["plan"]
  }
}

REST: POST /billing/setup — requires X-API-Key header.

saysigned_get_usage

Get current billing period usage.

{
  "name": "saysigned_get_usage",
  "description": "Get envelope usage for the current billing period, including count, cost, and plan details.",
  "inputSchema": { "type": "object", "properties": {} }
}

REST: GET /billing/usage — requires X-API-Key header.

Available Templates

Discover templates programmatically:

# List all templates
curl https://api.saysigned.com/templates

# Get template details with variable schema
curl https://api.saysigned.com/templates/nda_mutual_v1

nda_mutual_v1 — Mutual Non-Disclosure Agreement

Standard mutual NDA. Required variables: disclosing_party_name, receiving_party_name, effective_date, purpose, governing_law_state. Optional: term_years (default: 2), non_solicitation (default: false), etc.

service_agreement_v1 — Professional Services Agreement

Professional services contract. Required variables: client_name, provider_name, effective_date, scope_of_services, compensation_model, governing_law_state. Supports 4 compensation models: fixed, hourly, milestone, retainer.

Webhook Events

Configure your webhook_url during registration to receive real-time notifications.

Webhook Payload

{
  "event": "recipient.signed",
  "envelope_id": "env_...",
  "timestamp": "2026-02-01T12:00:00Z",
  "data": {
    "recipient_id": "rec_...",
    "recipient_name": "Alice Chen",
    "recipient_email": "alice@acme.com"
  }
}

Verifying Webhook Signatures

Every webhook includes an X-Signature-256 header containing sha256=<HMAC>. Verify it:

import hmac, hashlib

def verify_webhook(body: bytes, secret: str, signature_header: str) -> bool:
    expected = "sha256=" + hmac.new(secret.encode(), body, hashlib.sha256).hexdigest()
    return hmac.compare_digest(expected, signature_header)

Common Workflows

Two-Party NDA

1. POST /envelopes (template_id: "nda_mutual_v1", 2 signer recipients)
2. POST /envelopes/:id/send
3. Party A signs: POST /envelopes/:id/recipients/:r1/sign (X-Access-Token header)
4. Party B signs: POST /envelopes/:id/recipients/:r2/sign (X-Access-Token header)
5. → envelope.completed webhook fires, RFC 3161 timestamp anchored
6. POST /verify to confirm integrity

Service Agreement with CC

1. POST /envelopes (template_id: "service_agreement_v1", 2 signers + 1 CC)
2. POST /envelopes/:id/send
3. Both signers sign (in any order)
4. CC recipient receives notifications but doesn't sign
5. → envelope.completed on last signature

Handling Declines

1. Recipient declines: POST /envelopes/:id/recipients/:rid/decline
2. → recipient.declined webhook fires
3. → envelope.declined webhook fires (envelope status → declined)
4. Create a new envelope with revised terms if needed

Human Recipient Flow

1. POST /envelopes (set delivery_method: "email" on human recipients)
2. POST /envelopes/:id/send → invitation email sent to human
3. Human opens email → clicks "Review & Give Consent" link
4. Human reviews contract at doc.saysigned.com → gives consent or declines
5. → recipient.signed or recipient.declined webhook fires
6. Envelope auto-completes when all signers consent
7. Human receives confirmation email with 14-day document viewing link

Polling for Completion

If you don't use webhooks, poll for envelope completion:

1. Call GET /envelopes/:id (or saysigned_get_envelope) to check status
2. Poll every 5-10 seconds
3. Terminal states: completed, declined, voided
4. Max recommended wait: 24 hours

Error Handling

Security Notes

• API keys are shown once at creation. Store securely. Rotate or delete keys that are no longer needed.
• Config file security — API keys stored in MCP config files should have appropriate file permissions. Limit access to the config directory.
• Access tokens are per-recipient, per-envelope. Do not reuse. Tokens are 128-character hex strings with no expiration — treat them as secrets for the duration of the signing flow.
• Webhook secrets are per-agent. Verify every webhook signature.
• All connections require TLS (HTTPS). Verify TLS certificates for api.saysigned.com, mcp.saysigned.com, and doc.saysigned.com.
• API keys are stored as SHA-256 hashes — SaySigned never stores plaintext keys.
• URL tokens (email recipients) are 32-char HMAC-derived tokens, one-time use, cleared after consent.
• CSRF protection on consent/decline forms — tokens bound to recipient ID, expire after 4 hours.
• Rate limiting on consent pages — 10 URL attempts per 15 min per IP, 3 form submissions per 5 min per recipient.
• Sandboxing recommended — If running in an untrusted environment, enable logging/monitoring of config changes and outbound connections.

Legal Context

• ESIGN Act (15 U.S.C. § 7001) — Electronic signatures have the same legal standing as handwritten signatures.
• UETA Section 14 — Explicitly authorizes electronic agents to form contracts and conduct transactions.
• Attribution chain — Every signature records: who (name, email), when (timestamp), how (API, IP address, user-agent), and what (contract hash).
• RFC 3161 timestamp — Independent proof from DigiCert that the envelope was completed at a specific time.
• Hash chain — Tamper-evident audit trail where each entry links to the previous via SHA-256.
• ESIGN mandatory disclosures — four pre-consent disclosures displayed to human recipients: right to paper copies, right to withdraw consent, scope of consent (single document), and hardware/software requirements.
• AI-generated contract disclosure — if the contract was created from a template, a notice is displayed: "This document was prepared using automated tools based on the sender's inputs."

Pricing

Upgrade anytime: POST /billing/setup with {"plan": "payg"}, {"plan": "commit_500"}, or {"plan": "commit_2000"}. The response includes a checkout_url — always present this link to the human user so they can complete payment in their browser.