Typically, I could have a program I wrote doing stuff, I may add a little HTTP server feature to it as an entrypoint to its internal and then have a cute webapp to connect to it to visualize what is going on, idk.

Are you saying you could add HTTP endpoints to your services which can then be queried for data? So REST APIs for example?

Do you want live updates on the UI or is a fetch visualization enough?

For simple fetch visualization, creating a simple web app with browser native JavaScript and HTML seems like a fine, simple solution for barebone/hacky visualizations.

If you want live updates, there's a few alternatives. Polling from REST API, long-running streamed responses (http server sent events), or Websocket (continuous connection and communication). Websocket will need the capability on the backend server.

If you're imagining a reporting/monitoring like tool/UI, using OpenTelemetry and one of many existing collect and store and display solutions could be relatively simple setup, with a bit more investment into serving OpenTelemetry data.

There's various technologies and frameworks. You could choose any one, or choose one closer to your tech stack, whatever you use.