I've recently had to learn about fiduciary duty, and it struck me that this seems to apply to software developers. So my questions are

  1. Am I right in thinking that a developer has a fiduciary duty to the user?
  2. If so, what does this mean for a lot of software development organisations with business models that depend on software that does not entirely respect the interests of its users. For instance, would the developer of an ad-blocker who takes money from advertisers for allowing their adverts to bypass his block be considered in breach of this duty?

The rest of this post will explain my reasoning that this fiduciary relationship exists. Suppose that Alice writes some software and sells it to Bob to use. I happen to live in the UK, but from what I have read the same legal framework exists in many countries.

The Wex legal dicationary says:

Fiduciary duty is imposed whenever confidence is reposed on one side in a contractual relationship, so as to allow that side to exert influence and dominance over the other.

Bob is clearly reposing confidence in Alice here. Alice could have included hidden functionality in the program which would work to Bob's detriment. Bob has no practical way of finding out if Alice has done so. In effect Alice has been given control of a part of Bob's computer. In addition to the physical resources, Alice also has indirect access to information stored on the computer that Bob may wish to keep confidential. Alice has "influence and dominance" over those parts of the computer that her program can access.

The Free Dictionary says:

Courts have neither defined the particular circumstances of fiduciary relationships nor set any limitations on circumstances from which such an alliance may arise. [...]

A fiduciary relationship extends to every possible case in which one side places confidence in the other and such confidence is accepted; this causes dependence by the one individual and influence by the other.

I've seen lists of fiduciary relationships, but it is plain that all of these are illustrative rather than complete. It may be that a court has never found that a software developer has a fiduciary duty (Google hasn't turned up any), but there doesn't seem to be an obstacle to such a finding.

Looking at the second paragraph, it is clear that Bob has placed confidence in Alice. It is not necessarily clear that Alice has accepted such a relationship with Bob in particular, but it seems to me that

  1. By offering her program for sale, Alice has accepted a duty to her customers, and
  2. That this duty is a fiduciary one by the nature of the trust placed in her by her customers.

When Alice wrote the program she was unaware that Bob in particular was going to run it, so it would not be possible for Alice to know exactly what the interests of Bob are under all circumstances. However she will still have a clear understanding of the general interests of her users as a class, and she has a duty to act in those interests rather than her own.

  • "Software developer" is typically an individual who gets paid to develop software by some company, and follows the orders of that company. The software developer has responsibility towards the company employing or hiring him, but typically no responsibility to any users, unless covered by criminal law. You seem to be talking about the seller of software.
    – gnasher729
    May 16, 2023 at 8:04

1 Answer 1


You could certainly run the argument: it is unlikely to succeed.

Fiduciary duties are either specifically legislated (e.g. company directors) or involve a relationship of confidence (the obligation to keep secrets) as well as trust (e.g. lawyer, doctor).

Engineers (including software engineers) do not have this and AFAIK a fiduciary duty between an engineer and their client has never been found, even where the work is a one-on-one commission. For example, an engineer designing a bridge has the duties imposed by their contract to their client and a general common law duty e.g. the bridge won't fall down.

Where the engineering is for a mass market commercial product finding a fiduciary duty seems a vanishingly small possibility. The relationship lacks the intimacy required to create one. Reliance on a person's expertise is not enough - that's just a normal contractural or common law duty.

  • Can you expand on the distinction you make between confidence and trust? Also, do other areas of engineering share the element of "influence and dominance" created by running a program? Oct 14, 2016 at 21:55
  • An engineer who designs a bridge cannot find out anything about the people who drive across it. A software developer can insert code to obtain secret information from the people who run the program. Doesn't this imply a degree of confidence in the relationship? This is not a theoretical question: Google, for instance, seems to want to know where I am when I use the Android app store, but I regard that information as confidential. Oct 17, 2016 at 16:20
  • Do you have a source with your answer?
    – Mast
    Jul 12, 2017 at 7:23
  • I heavily agree and in addition it is not clear who the users even are. How can you have a fiduciary duty to someone you can not even identify?
    – emory
    Feb 10, 2019 at 17:03
  • That engineer building a bridge can install hidden microphones and cameras all over the bridge. Or automatic license plate readers and so on.
    – gnasher729
    May 16, 2023 at 8:06

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