Every microservices diagram starts clean and ends as a hairball. It is almost a law. You draw the services, you draw the calls between them, and within twenty boxes it is an unreadable mesh of crossing arrows that tells you nothing except "it is complicated." The problem is not the architecture. It is that the diagram is trying to show every connection at once, when what a reader needs is the shape: the boundaries, and the way services talk.
The way out is to stop drawing "every service calls every service" and instead draw two things deliberately: the boundaries that group services, and the communication style on each edge. Do that and even a large system stays legible.
Group by boundary, not by grid
The single biggest improvement you can make is to stop laying services out in a neat grid and start grouping them by the boundary they belong to. In domain terms these are your bounded contexts; in team terms they are usually who owns what. Ordering, Payments, Identity, Catalog. Draw those as labelled regions and drop the services inside them. Suddenly the diagram has structure, and a reader can navigate it by area instead of scanning forty identical boxes.
Show the communication style on every edge
Not all arrows are equal, and pretending they are is why microservices diagrams mislead. A synchronous request (one service calling another and waiting) has completely different failure and latency behaviour from an asynchronous event (one service publishing, others reacting whenever). Draw them differently: solid lines for synchronous calls, dashed for events through a bus or queue. Now the diagram tells an operational story. You can see where a slow service will cascade (the solid chains) and where the system is decoupled (the dashed hops).
Two kinds of arrow, drawn differently, turn a hairball into a map of where failure spreads and where it stops.
Draw data ownership, at least once
The rule that makes microservices microservices is that each service owns its data. A diagram that shows every service sharing one database is drawing a distributed monolith, whether the team means to or not. It is worth having one view where each service sits with its own store, because the moment two services point at the same database, you have found a coupling that will hurt later. You do not need this on every diagram, but you need it somewhere.
Add the edges that belong to everyone
A few components sit outside the boundaries and touch everything: the API gateway that fronts the whole system, the event bus or message broker that carries the asynchronous traffic, and, if you run one, the service mesh handling service-to-service concerns. Give these their own place at the edges of the diagram so they read as shared infrastructure, not as just another service in a box.
Resist the urge to draw everything
The failed microservices diagram tries to be complete. The useful one is deliberately partial. Pick the question the diagram answers, how a request flows, where the async boundaries are, which services own which data, and draw only what serves it. Complete-but-unreadable helps no one; focused-and-clear is the whole point.
Keep it alive
Microservices systems change faster than almost anything else you would diagram, new services, new events, retired dependencies. A hand-drawn version is stale before the sprint ends. Derive the skeleton from the source (specs, service manifests, or a call graph), regenerate as it evolves, and keep your boundary grouping and edge styling as the human layer on top. That way the diagram keeps up with a system whose whole promise is that it changes independently.
Group by boundary, style the edges by how services talk, show data ownership once, and generate the base so it stays current. That is a microservices diagram that clarifies instead of intimidates.