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Who published Adk Architecture?

Google (@google) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Adk Architecture by google — Agent Skill

Name: Adk Architecture
Rating: 4.2 (5 reviews)
Author: Google

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).

Google Updated Sep 9, 2026 14.4k repo stars

File contents

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`	`workflow/_dynamic_node_scheduler.py`
`ReplayManager` (resume scan)	`workflow/utils/_replay_manager.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`
`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.

---name: adk-architecturedescription: 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).--- # 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 `Event`s 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](references/interface-base-node.md) | | How does the graph schedule nodes, dedup dynamic children, propagate interrupts? | [Workflow](references/interface-workflow.md) | | How does a caller start an invocation? | [Runner](references/interface-runner.md) | | What is `Agent`, and which methods do I call on it? | [Agent](references/interface-agent.md) | | I am subclassing an agent — what do I override? | [BaseAgent](references/interface-base-agent.md) | | What is on an `Event`, and what may I assume about its lifetime? | [Event](references/interface-event.md) | | What does a node read and write on `ctx`? | [Context](references/architecture-context.md) | | Who creates the child Context, stamps events, retries, catches errors? | [NodeRunner](references/architecture-node-runner.md) | | Why are Runner, NodeRunner and Workflow three separate things? | [Runner roles](references/architecture-runner-roles.md) | | How does a human-in-the-loop pause and resume work for one node? | [Checkpoint and resume](references/architecture-checkpoint-resume.md) | | How does a whole workflow survive a pause, and what does `is_resumable` change? | [Workflow resumability](references/architecture-workflow-resumability.md) | | How are spans created, and what attributes do they carry? | [Observability](references/architecture-observability.md) | | Why does the model not see the raw event log? | [LLM context orchestration](references/architecture-llm-context-orchestration.md) | | Is this change a breaking change? Where does a new export belong? | [API principles](references/api-principles.md) | ## 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` | `workflow/_dynamic_node_scheduler.py` | | `ReplayManager` (resume scan) | `workflow/utils/_replay_manager.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` | | `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.

Frequently asked questions