A2A and MCP do not answer the same question
They are often named as competing options. They are not: one agent commonly uses both, at two different levels of its construction. This page says which does what, what KoPass measures of each, and why it refuses to put the two counts side by side.
A2A — between agents
Agent2Agent governs communication between agents built by different teams: discovering each other, delegating a task, following its execution. Announced by Google in April 2025, now under the Linux Foundation. It is a peer-to-peer interoperability protocol.
MCP — between an agent and its tools
Model Context Protocol governs an agent's access to what surrounds it: files, databases, APIs, services. The relationship is not peer to peer but client to server. An agent speaking A2A to its peers very probably speaks MCP to its tools.
What KoPass counts, and how
- A2A: public GitHub repositories carrying one of the protocol's declared topics. The filter is on declared topics, not on description text.
- MCP: entries in the official registry. The source alone delimits the ecosystem; no further filter is applied.
Why there is no comparison chart here
Because it would lie. The two counts do not cover the same population: one lists code repositories that declare themselves A2A, the other lists servers registered in a registry. A repository is not a server, and a registry entry is not a declared topic. Putting both numbers on one axis would produce a picture that is sharp and wrong. KoPass publishes each count on its own page, with its method and its date — and lets each remain what it is.