I think what you are ultimately getting at is: How do you ensure they write code the same way?. That isn’t a real problem and so it isn’t something you need to address. This comes up because insecurity is a very real concern.

Instead provide a business (not code) template to define requirements for integration. This should define what is needed in their documentation, what they output/return, their inputs, automation test requirements, and so forth. That list delicately does not include code style or any more of vanity. Most of this can be automated but you need code reviews to hold people to account and to use as a training opportunity. Be honest and critical during the code reviews. If people find respectful honesty offensive talk to them about it outside the group and if they still can’t get with it transfer them out of your team.

So you’re suggesting that one person decides that they like JQuery on the front end and one decides that they want to use plain Vanilla JS and one decides they like the look of Material UI, the other Bootstrap, and one happens to like sites that look like MySpace that’s ok?

And on the backend, if one developer liked log4net for logging, the other Serilog, and yet another developer likes to build his own logging framework that’s okay?

Let’s take this to a logical extreme, since one person is an old school VB developer and another likes F#, let’s just do that and throw in a little COBOL.Net for good measure....

And when a new dev comes in snsr takes forever to ramp up. No big deal. While we are at, let’s not follow the REST semantics either and no one needs those pesky frameworks like Express and ASP.Net. Let’s just go bare metal...

Or you could just have agreed upon standards....

If you’re going to have standards anyway, why not just use frameworks where you can open a req for the required framework that lets you get some developers who you can make sure already know the basics?

You’d be surprised at how many cheap developers you can get to throw together your yet another software as a service CRUD app using React.

> So you’re suggesting that one person decides that they like JQuery on the front end and one decides that they want to use plain Vanilla JS and one decides they like the look of Material UI, the other Bootstrap, and one happens to like sites that look like MySpace that’s ok?

The expectation is that developers are literate in their line of work, even though most companies don't hire like that. Since developers are expected to be literate don't waste time worrying about how to write code. If a developer suggests a tool that helps them on the "how to write the code" reject the tool.

Set business principles that specifically communicate the acceptable scope of work. Such principles can be something like this:

* code will execute within X milliseconds.

* code will allow up to X total dependencies (choose wisely).

* code will not exceed X bytes total size. If they want to include jQuery their code solution just increased 69kb.

The common failing is confusion around standards. Many developers find it easier if everybody just did everything the same way so that things appear standard. That approach ignores everything relevant to product quality and the goals of the business, which is stupid. It is stupid because it sacrifices simple for easy at the lowest level of leadership by lazy or weak managers. You don't get to offload management onto a framework and still hope to be a strong effective manager. Ultimately the success of a manager is tied to the work of that manager's team whether the team can retain/promote effective people.

When you set concrete and specific business limitations the limits are easily understood and based on objective criteria. Innovation and creativity are not stifled as developers are free to work within the constraints anyway they please.

This all makes sense once you accept that the group is worth more than the individual, but the product is worth more than the group. Sacrificing business goals for group cohesion is backwards just as sacrificing group integrity for an individuals option is backwards.

> You’d be surprised at how many cheap developers

That is also a common failure. Developers are never cheap unless you offshore. In hoping for cheap you will actually get developers that cost the same, do crappy work, don't value themselves, and that aren't valued by the organization. That is toxic. Instead hire people with potential to do great things and manage them effectively.