What is an “era”? Understanding MCP protocol ages

On ROKMCP we assign an “era” label to a server on every measurement. It’s a one-word health indicator summarizing which age of the MCP protocol that server speaks. Here’s what each one means.

modern

The server speaks the current MCP spec. The easiest to integrate and the most predictable type for an agent. This is the direction the ecosystem wants to go.

dual

Supports both the modern and the old protocol. The safest option during the transition period — it bridges to the new without breaking old clients.

legacy

Speaks only the old protocol. It may work, but it can cause compatibility issues with modern tools and becomes harder to support over time.

auth-gated

The server is up but behind an authentication wall — we can’t fully measure its schema without getting inside. The vast majority of the ecosystem is in this state. We’re working on solving these with standard OAuth.

unknown / unreachable

“unknown” — the server responds but we couldn’t clearly classify its protocol. “unreachable” — we can’t reach it at all: wrong address, broken certificate, or the server is down. Sometimes we say “unreachable” because the address looks wrong; we try to auto-correct these and find the real address.

Era shows not just the instant state of a single server, but where the whole ecosystem is heading: how fast is the migration from legacy to modern?