Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add agents/google/adk-docs/custom-agentsgit clone --depth 1 https://github.com/google/adk-docsWhat it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00000 | $0.12594 |
| Opus 5 | $0.00000 | $0.06297 |
| Sonnet 5 | $0.00000 | $0.02519 |
| Haiku 4.5 | $0.00000 | $0.01259 |
Grade A, and why
custom-agents scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 1,247 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Custom agent template workflows
Custom agents and agent-based workflows allow you to define arbitrary
orchestration logic by inheriting directly from BaseAgent and implementing
your own control flow. This approach allows you to create new execution patterns
similar to SequentialAgent, LoopAgent, and ParallelAgent, enabling you to
build highly specific and complex agentic workflows.
!!! warning "Alternative: graph-based workflows"
Starting in ADK 2.0, agent-based workflows using
`BaseAgent` have been superseded
by more flexible workflow structures, including
[graph-based workflows](/workflows/graphs/) and
[dynamic workflows](/workflows/dynamic/). You should
evaluate the capabilities of these workflow mechanisms
***before*** building a custom agent for your
target workflow.
!!! warning "Advanced Concept"
Building custom agents by directly implementing `_run_async_impl`, or its
equivalent in other languages, provides powerful control but is more complex
than using the predefined `LlmAgent` or `WorkflowAgent` types. We
recommend understanding those foundational agent types first before tackling
custom orchestration logic.
Overview
A Custom Agent is essentially any class you create that inherits from
google.adk.agents.BaseAgent and implements its core execution logic within the
_run_async_impl asynchronous method. You have complete control over how this
method calls other sub-agents, manages state, and handles events.
!!! Note
The specific method name for implementing an agent's core asynchronous logic may
vary slightly by SDK language, such as `runAsyncImpl` in Java, `_run_async_impl`
in Python, or `runAsyncImpl` in TypeScript. Refer to the language-specific API
documentation for details.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- yesterday First seen · 1,247 lines · 0 tokens per session scan A c1f6ca880f22
custom-agents is an agent published in the GitHub repository google/adk-docs (1,479 stars, last pushed 3d ago), licensed Apache-2.0. It costs nothing until one of its globs matches a file; then it loads 12,594 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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