I don't think you would be responsible for whether your software is used in a GDPR-compliant manner.
For GDPR compliance, it is important who the data controller is. The data controller is whoever determines the purposes and means of a personal data processing activity, i.e. the why and how. The data controller alone is responsible for their GDPR compliance. When a data controller wants to run some software, it's the data controller's responsibility to ensure that this software is used in a GDPR-compliant manner (or possibly not at all).
Determining purposes and means of processing
When someone other than the developer runs a software, the question is who might be a controller: you as the developer, they as the operator, or neither, or both?
The operator is clearly a controller: they determine a purpose for data processing (e.g. to manage staff) and have determined means to perform that processing (e.g. to use the software).
The developer may or may not be a controller.
Clearly, the developer has made choices about how the processing of personal data will be performed, i.e. has determined some means of processing. E.g. the developer has developed a particular architecture, chosen a way to store personal data, and has implemented some security measures. But determining some means is not sufficient to be a data controller, see discussion below.
Has the developer participated in determining the purposes of processing? I think this will depend on the specific functionality provided by the software in question. If the software just does what it says and processes the data for the operator's purposes, everything should be fine. If the software also processes data for the developer's purposes, that developer might be a controller. For example, if analytics or crash reports are collected by the developer, that would be a clear indication that the developer would be a (joint) controller.
So depending on specific factors, the operator might be the sole controller, or the operator and developer might be joint controllers.
Essential vs non-essential means
What about the developer determining some means? When does this make the developer a joint controller? The EDPB has created a theory of essential vs non-essential means:
40. As regards the determination of means, a distinction can be made between essential and non-essential means.
“Essential means” are traditionally and inherently reserved to the controller. While non-essential means can also be determined by the processor, essential means are to be determined by the controller.
“Essential means” are means that are closely linked to the purpose and the scope of the processing, such as
- the type of personal data which are processed (“which data shall be processed?”),
- the duration of the processing (“for how long shall they be processed?”),
- the categories of recipients (“who shall have access to them?”) and
- the categories of data subjects (“whose personal data are being
Together with the purpose of processing, the essential means are also closely linked to the question of whether the processing is lawful, necessary and proportionate.
“Non-essential means” concern more practical aspects of implementation, such as the choice for a particular type of hard- or software or the detailed security measures which may be left to the processor to decide on.
– EDPB guidelines 07/2020 on the concepts of controller and processor in the GDPR,
added formatting for legibility
Looking through that list of essential means, some might be determined by a software's developer, but I wouldn't expect this to be the case for this kind of open source software.
types of personal data: the software certainly sets a framework for processing specific kinds of personal data, e.g. by providing database fields for names, contact details, and schedules. But ultimately, the developer does not control which data is actually collected and filled into those fields – the developer does not cause specific kinds of personal data to be processed with the system.
duration of processing: unless the software is programmed with a fixed retention schedule, it should be impossible to argue that the developer has determined the duration of processing. Even then, it would also be the operator who has determined this duration to be appropriate, rather than editing the open-source software to change the duration. But typically, no such retention schedule is enforced, and retention would depend solely on the operator (who can use an admin interface or a database console to erase old records).
categories of recipients: typically, the developer does not determine to whom the data in the system will be given. But if the system sends data to third parties by itself, this might change. For example, if the system is pre-configured to store data in an existing cloud database instance, or to a specific analytics server, the developer might be acting as a controller.
Here, good software engineering and legal risk minimization coincide. Best practices for web apps state that account credentials and connection strings shouldn't be hardcoded or committed to a repository, and should instead be provided externally (e.g. via environment variables).
categories of data subjects: this depends solely on how the software is used. The developer has no way to determine whose data the operator will enter into the system.
If the developer isn't a controller, might they be a data processor instead?
In a GDPR context, a data processor is whoever processes personal data on behalf of a controller. The developer is clearly not a processor in this scenario because both the “processing” and “on behalf” criteria fail.
- The developer has no access to the data in the operator's instance, so cannot process the personal data.
- There is no direct relationship between the developer and the operator. The operator has not delegated authority to the developer so that the developer would be acting “on behalf” of the operator. There is a legal relationship between the two roles (the developer has licensed the software to the operator) but that is entirely irrelevant in a data protection context.
The GDPR isn't directly about cookies
While the GDPR does cover how personal data can be processed with cookies, the famous “cookie law” is actually separate: those cookie consent requirements stem from EU member state's implementations of the ePrivacy directive. Instead of talking about “controllers”, ePrivacy has concepts such as the “provider of an information society service”. While this role fits perfectly to an operator/provider who runs a web app in a publicly accessible manner, it does not fit a developer who merely makes some source code available.
Is the developer even subject to the GDPR?
The GDPR can only apply to data controllers and processor who process personal data. As discussed above, the developer is probably not processing personal data at all. Even if the developer were processing personal data, it is questionable if GDPR would apply assuming the developer has no “establishment” in the EU (e.g. an office). Then, the question would be whether those processing activities are either related to offering goods or services to data subjects in Europe, or whether the processing activities involve monitoring the behavior of people who are physically in Europe. Unless the developer is actively targeting European businesses with marketing for this software, the answer is very likely “no”.
Could the operator sue the developer for providing software that isn't GDPR-compliant?
The operator can sue anyone for any reason, but is probably not going to win. As discussed, the operator is a data controller. They are responsible for ensuring that their purposes and means are GDPR-compliant. That involves selecting suitable software. The data controller would be neglecting their own responsibilities if they just download some random software and start feeding personal data into it.
Things might be different if the operator specifically advertises GDPR compliance features but you're not going to do that.
It's also worth noting that common open source licenses like the Apache License 2.0 include a warranty and liability disclaimer. To which degree they protect the developer ultimately depends on national laws, but they make it difficult for the operator to make a legal argument that they're entitled to a GDPR-compliant product. See also the related question: Do warranty disclaimers in software licenses carry any legal weight?
What can you do?
First, don't worry too much. Given how much bad software there is on the internet, surprisingly few developer get into legal trouble for writing source code that's buggy or missing some features.
Second, consider choosing a license for your project that includes a reasonable warranty/liability disclaimer.
Third, make the state of your project clear in your README file. If someone knows that this is alpha-quality software and that no compliance features were implemented, it's their own fault if they actually use that software.