Open-source e-signature APIs and signing libraries
We track 9 open-source e-signature platforms and signing libraries, each checked for licence, commercial use, hardware, paid services and setup. pyHanko runs on your own machine, allows commercial use and needs no paid service. Easiest to set up: pyHanko, JSignPdf and endesive (and 1 more).
Facts checked 7 Nov 2026. Each project’s page shows the source and date for every answer.
There are two kinds of tool here. DocuSeal, Documenso, OpenSign and LibreSign are full signing platforms. You upload a document, add signers and send it, and their docs describe an API for doing that from your own app. pyHanko, endesive and the EU's DSS are developer libraries that add certificate signatures to PDFs inside your code, with no sending or tracking. Open PDF Sign and JSignPdf sit between the two, as a command-line tool and small server.
Several platforms are AGPL or keep some features in a paid edition, so check the commercial-use column before building a product on one.
Compared
| Compare | Project | Runs on my machine | Allowed at work | Paid services | Setup | Runs on | Stars |
|---|---|---|---|---|---|---|---|
| DocuSealSelf-hostable app to build PDF forms and have them filled and signed by multiple people, with email, API and webhooks; some features are paid Pro. | Yes | ConditionsAGPL-3.0 | Optional only | Medium | Not confirmed | 19k | |
| DocumensoSelf-hostable document signing platform with signing order, reminders, templates, audit logs and an API; AGPL core plus paid Enterprise features. | Yes | ConditionsAGPL-3.0, open core | Optional only | Medium | Not confirmed | 16k | |
| OpenSignSelf-hostable PDF e-signing with multiple signers in sequence, OTP checks, templates, audit trail with completion certificate, and an API. | Yes | ConditionsAGPL-3.0 | None required | Medium | Windows, macOS, Linux | 7.3k | |
| DSS (Digital Signature Service)European Commission Java library for creating, extending and validating advanced electronic signatures (XAdES, CAdES, PAdES, JAdES). | Yes | ConditionsLGPL-2.1 | None required | Hard | Windows, Linux | 1.1k | |
| pyHankoPython library and CLI that signs, stamps, validates and encrypts PDFs with certificates, PKCS#11 tokens, timestamps and PAdES profiles. | Yes | YesMIT | None required | Easy | Windows, macOS, Linux | 799 | |
| JSignPdfDesktop and command-line app that adds certificate-based digital signatures to PDFs, with smartcard/HSM support, timestamps and PAdES. | Yes | ConditionsMPL-2.0 or LGPL-2.1 | None required | Easy | Windows, macOS, Linux | 491 | |
| LibreSignNextcloud app for document signing workflows with signing order, internal and external signers, reminders, certificates and validation. | Yes | ConditionsAGPL-3.0-or-later | None required | Medium | Not confirmed | 845 | |
| endesivePure-Python library to create and verify certificate signatures in PDFs, S/MIME email, XML (XAdES) and plain files, with PKCS#11/HSM support. | Yes | ConditionsMIT | None required | Easy | Windows | 277 | |
| open-pdf-signJava command-line tool and small HTTP server that adds PAdES certificate signatures to PDFs, visible or invisible, with optional timestamps. | Yes | ConditionsApache-2.0 | None required | Easy | Not confirmed | 953 |
Tick up to three to compare them side by side. Ordered by our ranking (stars 40%, recent activity 30%, how many facts we could source 30%), so a well-documented, active project can sit above a bigger one. Unknown means we found no source, never a yes. Stars show attention, not quality. How we check and rank.
Where to start, by what matters to you
Each one comes from a sourced fact on the project’s page, not from a sponsor or a test score.
Common questions
Is there a free alternative to the DocuSign API?
Yes. OpenSign, DSS (Digital Signature Service), pyHanko, JSignPdf, LibreSign and endesive (and 1 more) need no paid service at all. DocuSeal and Documenso are free to run, with paid services optional or depending on your setup. The software is free; what you may pay for is the server it runs on and any outside service it relies on, which the paid-services column lists.
Does DocuSign have an API?
Yes. DocuSign's eSignature REST API lets your own app request signatures, automate forms and track documents; its docs describe more than 400 endpoints. The open-source tools here give you a signing API you host yourself instead. Source: developers.docusign.com.
Can I self-host an e-signature API?
6 of the 9 can run on your own server: DocuSeal, Documenso, OpenSign, DSS (Digital Signature Service), LibreSign and open-pdf-sign. DocuSeal, Documenso and OpenSign document a Docker setup. Setup is rated easy for open-pdf-sign.
What server does a self-hosted e-signature tool need?
Memory stated in their docs: 1 GB for Documenso. The others give no single figure. Each project page quotes the source and says whether a figure is a minimum or a recommendation.
Which can I use in a commercial product?
Confirmed: pyHanko (MIT). With conditions: DocuSeal, Documenso, OpenSign, DSS (Digital Signature Service), JSignPdf, LibreSign, endesive and open-pdf-sign. This is not legal advice; read each licence.
Which is easiest to set up?
Rated easy from their install docs: pyHanko, JSignPdf, endesive and open-pdf-sign. Each page links the exact install step we checked.
Which run on Linux?
OpenSign, DSS (Digital Signature Service), pyHanko and JSignPdf are documented to run on Linux. The others are web apps, servers or unconfirmed; check each page.
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