Build a Cross-Language Multi-Agent Team with ADK and A2A

A Google Developers Blog guide (Shubham Saboo & Eric Dong, 2026-06-22) that turns the A2A “agent → agent across vendors/frameworks” claim into a worked cross-language example: a contract-compliance pipeline whose agents are written in different languages and collaborate over A2A without rewrites.

The worked example

• Python extraction agent — Gemini parses a legal contract and extracts key terms.
• Go compliance validator — a deterministic, language-native rules engine; plain HTTP, no AI framework — it’s A2A-compliant by protocol adherence alone.
• Python report agent — writes the audit summary.
• A Python ADK orchestrator chains them with SequentialAgent, wrapping the Go service as a RemoteA2aAgent — a remote A2A endpoint consumed as a local sub-agent, no custom HTTP client.

Why it matters here

• A2A’s thesis, demonstrated. The spoke pages A2A as the agent↔agent wire format that lets orchestrator → subagent fan-out span different builders. This is the first concrete instance: the Go validator is a different language (and no AI framework), yet plugs into a Python ADK orchestrator purely via A2A’s three mechanisms — Agent Cards at /.well-known/agent.json (discovery), JSON-RPC 2.0 message/send over one HTTP endpoint (communication), and Tasks with submitted/working/completed/failed states (lifecycle). It moves “decompose the monolith into per-language microservice agents” from slideware to a runnable pattern.
• Resilience as a first-class state. The pipeline carries explicit checkpoints (INGESTED → EXTRACTED → COMPLIANCE_PENDING …); when the Go agent is unreachable it transitions to MANUAL_REVIEW (human fallback) rather than failing — the reversibility/recovery discipline expressed at the orchestration layer, and a durability concern made concrete.
• Standards-layer governance, again. ADK consuming A2A this cleanly reinforces the recurring pattern: Google builds the spec, donates it to the Linux Foundation, then ships first-party tooling (RemoteA2aAgent) that makes the open standard the path of least resistance.

Caveats

First-party Google guide (T1 for the mechanism), but it’s a tutorial/marketing artifact — it shows A2A’s best case, not adoption breadth or interop against rival schemes (ACP, vendor-native). Languages shown are Python + Go; ADK’s full cross-language support isn’t enumerated.

Related

a2a-protocol · adk · agent-orchestration · agent-guardrails · durable-agents · agentic-resource-discovery · google