OpenSign

OpenSign is an open-source PDF signing service for individuals and organizations that need reusable templates, developer workflows, or the option to host the software themselves. Its free plan is unusually broad on signatures and templates, while monthly invitation limits and paid gates on production API use narrow its fit for higher-volume work.

Overview

OpenSign handles document signing, storage, and security, with completion certificates, sequential signing, email notifications, and OpenSign Drive included in its free plan. The combination makes it practical for recurring, low-volume signing where a template can save setup time. The free plan allows up to 15 invitation emails per month, though, so unlimited digital signatures do not mean unlimited sending capacity.

Security measures include TLS-encrypted transport, audit trails, IP logging, and tamper-evident signed PDFs. Two-factor authentication and passkey sign-in provide additional account protections. These controls make OpenSign a considered option for workflows that need traceable document handling, while the invitation cap still matters for teams sending regularly.

Key features

Templates and signing workflows

Users can prepare templates with pre-placed widgets and reuse them for repeat documents. The API supports self-signing, drafts, signer roles, and real-time webhook notifications. Signature order can be sequential or allow signers to act in parallel, giving teams room to match different processes. Public template links and bulk sending require a paid plan, so the free tier is less suitable when recipients need an open link or many documents must go out together.

API and integrations

Templates can be embedded in React, Next.js, HTML, JavaScript, and Angular projects, which suits teams adding signatures to their own web experiences. Sandbox API tokens are available on every plan for development, but live API tokens require Professional or Teams. That distinction gives developers a way to build and test before committing to a production plan; it also means the free tier cannot run a live API workflow.

Email and hosting

OpenSign supports configurable SMTP, including Gmail and third-party providers, although some SMTP features are limited to paid plans. Docker self-hosting instructions cover Linux, macOS, and Windows, giving organizations the option to manage deployment themselves. Self-hosting is a meaningful choice for teams with the capacity to run software; those wanting a managed setup may prefer to assess the hosted plan limits first.

Pricing

OpenSign uses a freemium model. The Free plan costs nothing and includes unlimited digital signatures, unlimited templates, completion certificates, sequential signing, OpenSign Drive, and email notifications. Its practical constraints are up to 15 invitation emails a month, no bulk sending or public links, and no live API tokens. It suits personal use and modest recurring workflows, but the invitation allowance may be restrictive for busy teams.

Professional and Teams have custom pricing. Professional includes 240 API signatures per year, up to 10 signers per document, and up to 240 bulk documents. Teams raises those allowances to 500 API signatures per year and up to 500 bulk documents, while retaining the 10-signer limit. These plans are the relevant step up for production API access or batch sending; the higher Teams quotas favor greater annual volume. Enterprise also has custom pricing and adds a custom domain, whitelabeling, an uptime SLA, SSO support, and priority support, making it the plan for organizations that need those deployment and support provisions.

Platforms

OpenSign supports web use and provides API access, with self-hosting instructions for Linux, macOS, and Windows. This mix suits both browser-based signing and teams integrating the service into software or managing their own deployment.

Who it's for

OpenSign suits individuals and businesses, from startups to large corporations, when reusable templates or embedded signing workflows are useful. It is particularly compelling for developers who need to build around the API and for organizations that want a self-hosting option. People who need bulk sending, public template links, or live API access should budget for a paid plan; occasional senders can start with Free if 15 invitation emails per month is enough.

Pros and cons

• Pros: The free plan includes unlimited signatures and templates, plus completion certificates and OpenSign Drive, making it useful for repeat low-volume signing without a per-signature allowance.
• Pros: Templates, webhook notifications, multiple signer roles, and framework embedding give developers several ways to fit signing into an existing workflow.
• Pros: Docker self-hosting instructions span Linux, macOS, and Windows, and security features include audit trails and tamper-evident PDFs.
• Cons: Free users are capped at 15 invitation emails per month and cannot use bulk sending or public links, limiting larger or open-link workflows.
• Cons: Production API tokens start with Professional or Teams, so sandbox availability does not make the free plan suitable for a live API integration.
• Cons: Professional, Teams, and Enterprise use custom pricing, making the cost of scaling difficult to compare in advance.

Alternatives

PandaDoc is a freemium alternative with a free plan that includes a yearly allowance of 60 documents and supports Android, iOS, web, and API access; consider it if those platform options or its stated document allowance better fit your needs.

Dropbox Sign API offers a free package of up to 3 signature requests per month and a separate test mode; it may suit a developer whose free production allowance is sufficient.

Signater has a free plan capped at 3 envelopes per month, with one user and up to 3 signers per envelope; it is an option for very occasional signing.

Skribble offers a free Starter plan with pay-per-signature pricing and stated SES, AES, and QES rates; consider it if that pricing structure matches your signing needs.

Xodo Sign has a free plan with one document per week, one signer, one seat, and no active templates; it may fit a narrower, low-volume workflow.

BoldSign offers a free Essential plan with 25 envelopes per month, two templates, and one user; it may suit users who need a defined monthly envelope allowance.

PearSign has a free plan with 3 envelopes per month, 3 templates, and one user, making it another option for occasional use.

Documenso is an open-source alternative with API, self-hosted, and web support.

For broader comparisons, see Digital Signature API Software, E-Signature Software, and Electronic Signature Software.

Verdict

Choose OpenSign if you want a free way to sign recurring documents with reusable templates, or need API-driven signing and the ability to self-host. Its security features and workflow options give it substance beyond basic signing, but the free tier's 15-email monthly cap and the paid requirement for live API access, bulk sending, and public links are decisive constraints. If your workflow depends on those capabilities, compare the custom-priced paid plans before adopting it.