OpenSign is a self-hostable, open source alternative to commercial e-signature platforms like DocuSign, Adobe Sign, and PandaDoc. It enables individuals and organizations to securely sign, annotate, and manage PDF documents without vendor lock-in or subscription fees. Built for developers, legal teams, and small businesses, OpenSign solves the problem of costly and restrictive e-signature solutions by offering full control over data and workflows.
The platform is built with React.js for the frontend, Node.js and MongoDB for the backend, and supports deployment via Docker or DigitalOcean. It includes a RESTful API, Zapier integration, and a secure document vault called OpenSign™ Drive. All features are available in the free tier, with no limits on the number of signatures.
What You Get
- Secure PDF E-Signing - Uses robust encryption to sign PDFs with hand-drawn, typed, or uploaded signatures, with end-to-end security and compliance.
- Annotate Documents - Advanced signing pad supports hand-drawn signatures, image uploads, typed text, and saved signature templates for flexible signing.
- Multi-signer Support - Invite multiple signers with customizable signing order, sequence enforcement, and link-based access without requiring accounts.
- Email OTP Verification for Guest Signers - Guest users must verify their identity via a one-time code sent to their email before signing, ensuring document integrity.
- PDF Template Creation - Create, store, and reuse PDF templates with pre-defined signature fields to streamline recurring signing workflows.
- OpenSign™ Drive - Centralized, secure cloud storage for organizing, sharing, and archiving signed and unsigned documents with folder hierarchies.
- Audit Trails & Completion Certificates - Automatically generates detailed logs including timestamps, IP addresses, email IDs, and phone numbers; provides a tamper-evident completion certificate per signed document.
- API Support - Full REST API with key-based authentication and documented endpoints for integrating e-signature workflows into CRM, ERP, or custom systems.
- Zapier Integration - Connect OpenSign to 5,000+ apps via Zapier to automate document signing workflows across tools like Google Drive, Notion, or Salesforce.
- Customizable Email Templates - Modify the design and content of signing invitations, reminders, and completion notifications to match your brand.
Common Use Cases
- Running a legal practice - A small law firm uses OpenSign to send client contracts for e-signature, store signed documents securely in OpenSign™ Drive, and generate audit certificates for compliance.
- Managing HR onboarding - An HR team automates offer letter signing by creating templates, inviting candidates via email with OTP verification, and storing signed documents in a secure folder structure.
- Integrating e-signatures into a SaaS product - A startup embeds OpenSign’s API to allow users to sign service agreements directly within their application without leaving the platform.
- Self-hosting a document signing solution - A government agency deploys OpenSign on-premises using Docker to maintain full data sovereignty and avoid third-party cloud vendors.
Under The Hood
Architecture
- Monorepo structure cleanly separates frontend (Next.js) and backend (Express-like) applications, enabling focused development domains
- Docker-based orchestration enforces service boundaries between client, server, database, and reverse proxy, though business logic remains tightly coupled with UI and API layers
- No explicit service or repository patterns observed, leading to minimal abstraction and direct component-to-database dependencies
- Dependency injection is implicitly handled via environment variables at build time, with no dedicated DI container or configuration management system
Tech Stack
- Frontend built with React, Next.js, and TypeScript, leveraging @mui for UI components and react-pdf for document rendering
- Backend powered by Parse Server with MongoDB as the primary data store, deployed via official Docker images
- Infrastructure is defined through docker-compose, Caddyfile for TLS and routing, and volume mounts for persistent storage
- Build automation relies on Makefile and npm scripts, with no state management or API client abstractions implemented
Code Quality
- Extensive testing coverage exists but lacks depth in validating business logic, with integration and unit tests poorly differentiated
- Error handling is generic and inconsistent, with no custom error classes or structured error propagation
- Type safety is absent, increasing susceptibility to runtime errors and reducing maintainability
- Linting and formatting rules are minimally configured, with no enforceable standards for security, performance, or code clarity
What Makes It Unique
- Native browser-based PDF annotation and e-signature workflow with drag-and-drop widget placement, eliminating server-side rendering dependencies
- Dynamic email template system powered by URL hash-based JSON configurations, enabling shareable, stateful designs without backend storage
- Unified form and email builder with synchronized styling engine that maintains consistent typography and layout across document and email interfaces
- Real-time drag previews for form widgets that dynamically scale fonts and render interactive elements directly in the drag layer based on page context