What is the primary distinction between MCP and Google's A2A protocol?
MCP connects an agent to tools and data; A2A connects an agent to other agents. Different layers, complementary, not competing.
Picture a worker at a desk. MCP is the worker reaching for tools on the desk: a calculator, a filing cabinet, a printer. It is how one worker grabs and uses equipment. A2A is two workers talking across the office to split a job: 'You handle the invoices, I'll draft the report, send me yours when done.' One protocol is about a single agent picking up tools. The other is about agents coordinating and delegating work to peers. They never fight over the same job. A real system uses both at once: each agent uses MCP to touch its own tools, and the agents use A2A to hand tasks back and forth.
Detailed answer & concept explanation~8 min readEverything you need to truly understand this topic: intuition, mechanics, step by step explanation, code, formulas, and worked example. Click to expand.
Everything you need to truly understand this topic: intuition, mechanics, step by step explanation, code, formulas, and worked example. Click to expand.
Everything you need to truly understand this topic: intuition, mechanics, step by step explanation, code, formulas, and worked example.
Everything important, quickly.
3 min: two-axis framing (vertical MCP vs horizontal A2A) + what each boundary crosses + both open + one stack that uses both together.
| Concern | MCP | A2A |
|---|---|---|
| Boundary | Agent to tools and data | Agent to peer agent |
| Core question | How does an agent access capabilities? | How do agents delegate and coordinate? |
| Unit of interaction | Tool call, resource read, prompt | Task with messages and artifacts |
| Discovery | tools/list, resources/list | Agent Card at well-known URL |
| Openness | Open spec, Anthropic origin | Open spec, Google origin |
| Relationship | Complementary, lower layer | Complementary, peer layer |
Real products, models, and research that use this idea.
- Google introduced A2A in 2025 with partners, positioning it as complementary to Anthropic's MCP rather than a replacement.
- An orchestrator agent delegates a research subtask to a specialist agent via A2A, and that specialist queries Postgres through an MCP server.
- A2A's Agent Card published at a well-known URL lets one agent discover another's skills, much as MCP's tools/list discovers tool catalogs.
What an interviewer would ask next. Try answering before peeking at the approach.
QWalk me through a system where an agent uses both MCP and A2A in a single workflow.
QWhy is modeling a remote agent as just another MCP tool a poor design choice?
Don't say thisRed flags and common mistakes that signal junior thinking. Click to expand.
Red flags and common mistakes that signal junior thinking. Click to expand.
Framing A2A as a newer or rival version of MCP. They span different boundaries, so a real stack runs both side by side.
The night-before-the-interview bullets. Scan these on the way to the call.
Primary sources. Skim if you want the original framing.
Same topic, related formats. Practice these next.