Authenticate using HTTP Basic auth with your Dropbox Sign API key as the username and an empty password, or use OAuth 2.0 for third-party apps; the API key is available in Dropbox Sign Settings > API.
Retrieve template IDs via GET https://api.hellosign.com/v3/template/list; the response includes template metadata, defined roles (signer roles), and merge fields.
Send a signature request from a template by POSTing to https://api.hellosign.com/v3/signature_request/send_with_template with form-encoded or JSON body containing 'template_id', 'subject', 'message', and 'signers' array.
Each signer in the array must include 'role' (matching a role defined in the template), 'name', and 'email_address'; multiple signers can be included if the template has multiple roles.
Pre-fill custom fields by including 'custom_fields' array in the request body with 'name' matching the field name in the template and 'value' containing the pre-filled text.
Monitor status by configuring a callback URL in Dropbox Sign Settings to receive event webhooks; events include 'signature_request_signed', 'signature_request_all_signed', and 'signature_request_declined'.
Known gotchas
Dropbox Sign was rebranded from HelloSign after Dropbox's acquisition, and the API domain remained api.hellosign.com for backward compatibility — documentation and the actual endpoint domain currently coexist under both brand names; use api.hellosign.com in code.
Test mode requests (include 'test_mode=1' in the request body) do not send real emails and do not count against your signature quota, but test mode signatures cannot be converted to real signatures after the fact — always verify test vs. production mode before sending.
Template roles are case-sensitive and must match exactly; if a template defines a role 'Client' and you send with role 'client', the API may return an error or silently not assign the signer, depending on the version.
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp