adk-architecture
Explains how the ADK runtime fits together: the node and graph execution model, Context and Event flow, checkpoint and resume, tracing, and the rules governing the public API surface. Use when answering "how does X work" about ADK internals, tracing where an event or a piece of state comes from, deciding where a new capability belongs, reviewing a change to BaseNode, Workflow, Runner, Agent, Event or Context, working out why a node re-ran or stayed waiting after a resume, or judging whether a change breaks the public API. Don't use for assembling an agent from existing pieces (use adk-agent-builder), diagnosing one failing run or test (use adk-debug), or formatting and naming conventions (use adk-style).
How do I install this agent skill?
npx skills add https://github.com/google/adk-python --skill adk-architectureIs this agent skill safe to install?
- Gen Agent Trust Hubpass
This skill provides architectural documentation and technical reference materials for the ADK (Agent Development Kit) runtime. It describes the internal execution model, event flow, and API principles in a purely informative manner.
- Socketpass
No alerts
- Snykpass
Risk: LOW · No issues
What does this agent skill do?
ADK Architecture
The runtime is a graph of nodes. BaseNode is the unit of execution.
Workflow is a node that schedules other nodes along declared edges.
NodeRunner executes exactly one node. Runner owns the invocation and the
session. Agents are nodes too — BaseAgent extends BaseNode.
A node communicates with its parent through a per-execution Context, and
with the session through Events it yields. Those are two separate channels:
ctx carries the result upward, events carry persistence and streaming.
Read the source before relying on any signature here. These notes drift; the
code does not. Paths below are relative to src/google/adk/.
Pick a reference
| Question | Reference |
|---|---|
| What must a node implement? What may it yield? Which config fields exist? | BaseNode |
| How does the graph schedule nodes, dedup dynamic children, propagate interrupts? | Workflow |
| How does a caller start an invocation? | Runner |
What is Agent, and which methods do I call on it? | Agent |
| I am subclassing an agent — what do I override? | BaseAgent |
What is on an Event, and what may I assume about its lifetime? | Event |
What does a node read and write on ctx? | Context |
| Who creates the child Context, stamps events, retries, catches errors? | NodeRunner |
| Why are Runner, NodeRunner and Workflow three separate things? | Runner roles |
| How does a human-in-the-loop pause and resume work for one node? | Checkpoint and resume |
How does a whole workflow survive a pause, and what does is_resumable change? | Workflow resumability |
| How are spans created, and what attributes do they carry? | Observability |
| Why does the model not see the raw event log? | LLM context orchestration |
| Is this change a breaking change? Where does a new export belong? | API principles |
Where the code lives
| Concept | Module |
|---|---|
BaseNode, START | workflow/_base_node.py |
Workflow, _LoopState | workflow/_workflow.py |
Graph, edge compilation | workflow/_graph.py |
NodeRunner | workflow/_node_runner.py |
DynamicNodeScheduler, DynamicNodeState, DynamicNodeRun | workflow/_dynamic_node_scheduler.py |
ReplayManager (resume scan) | workflow/utils/_replay_manager.py |
check_interception (replay fast-forward) | workflow/utils/_replay_interceptor.py |
NodeInterruptedError, NodeTimeoutError | workflow/_errors.py |
Context, ctx.run_node() | agents/context.py |
ReadonlyContext | agents/readonly_context.py |
InvocationContext | agents/invocation_context.py |
BaseAgent, LlmAgent (aliased Agent) | agents/base_agent.py, agents/llm_agent.py |
BaseLlmFlow, SingleFlow, AutoFlow, flows/llm_flows/ subpackages (context/, prompt/, tools/, extensions/, core/) | flows/llm_flows/ |
Event, NodeInfo | events/event.py |
EventActions | events/event_actions.py |
Branch paths (parent.child@1) | events/_branch_path.py |
Node paths (wf@1/child@2) | events/_node_path_builder.py |
Runner, InMemoryRunner | runners.py |
LiveRequestQueue, LiveRequest | live/live_request_queue.py |
Node spans, TelemetryContext | telemetry/node_tracing.py |
ResumabilityConfig | apps/_configs.py |
Everything under workflow/ is a leading-underscore module. Treat those names
as internal — they can change without a major version bump, so a change there
is not automatically a breaking change.
How can the creator link this skill?
Add the canonical catalog link to the repository README so users can inspect current installs and available audits. The publishing guide covers the complete discovery path.
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