Koog 1.0 idioms, gotchas, and scaffolding skills for Kotlin agents on the JVM
88
88%
Does it follow best practices?
Impact
88%
1.95xAverage score across 43 eval scenarios
Passed
No known issues
This skill is an action router — pick the step that matches the user's intent and execute only that step. Do not run other steps; do not parallelize.
Available actions:
nodeLLMRequestStreaming)nodeLLMRequestMultipleChoices)nodeLLMModerateText / nodeLLMModerateMessage)nodeLLMRequestForceOneTool)Use when the caller needs to see partial output as it arrives (Ktor server endpoint, CLI with live print, conference demo with text appearing live).
val strategy = strategy<String, String>("stream-reply") {
val streamReply by nodeLLMRequestStreaming { chunk ->
// chunk-handler — runs on every streamed chunk
print(chunk.text)
}
edge(nodeStart forwardTo streamReply)
edge(streamReply forwardTo nodeFinish)
}The chunk-handler lambda runs synchronously on every streamed delta. Don't block inside it — the LLM's stream stalls if the handler is slow. For network I/O (writing chunks to a Ktor response), use a channel/flow downstream rather than calling respond* directly inside the handler.
Streaming doesn't compose with tool calls in the same node — for "stream the reply text but still allow tool calls", use a singleRunStrategy shape and stream from nodeLLMRequestStreaming only on the text-reply branch.
Finish here.
Use when you want multiple completions for the same prompt and downstream code (or a critic node) picks the best.
val strategy = strategy<String, String>("sample-and-pick") {
val sample by nodeLLMRequestMultipleChoices(numChoices = 3)
val pick by node<List<Message.User>, Message.User>("pick-best") { choices ->
// pick logic — e.g., longest reply, or run a critic LLM
choices.maxBy { it.content.length }
}
edge(nodeStart forwardTo sample)
edge(sample forwardTo pick)
edge(pick forwardTo nodeFinish transformed { it.content })
}Each choice costs one LLM completion at full token rates — sample 3 for 3× the cost. Use when the picker's signal is cheaper or more reliable than the per-completion quality.
Finish here.
Two variants:
nodeLLMModerateText() — String inputnodeLLMModerateMessage() — Message.User inputBoth call a moderation classifier (provider-dependent) and produce a moderation result that downstream edges branch on.
val strategy = strategy<String, String>("moderated-chat") {
val moderate by nodeLLMModerateText()
val safeReply by nodeLLMRequest()
edge(nodeStart forwardTo moderate)
edge(moderate forwardTo nodeFinish onCondition { it.flagged } transformed { "I can't help with that request." })
edge(moderate forwardTo safeReply onCondition { !it.flagged })
edge(safeReply forwardTo nodeFinish onTextMessage { true })
}The moderation node returns a typed result with a flagged boolean and category breakdown — branch on flagged to short-circuit, and on categories if you need finer-grained handling.
Finish here.
Use when the next step must invoke a specific tool — no LLM choice, no fallback to text. Common case: a "router" agent where the first step always calls classify_intent.
val classifyTool = ClassifyIntentTool()
val strategy = strategy<String, String>("force-router") {
val forceClassify by nodeLLMRequestForceOneTool(classifyTool)
val execute by nodeExecuteTools()
val followUp by nodeLLMSendToolResults()
edge(nodeStart forwardTo forceClassify)
edge(forceClassify forwardTo execute)
edge(execute forwardTo followUp)
edge(followUp forwardTo nodeFinish onTextMessage { true })
}The forced tool must already be in the agent's ToolRegistry. Forcing a tool not in the registry is a runtime error.
Finish here.
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skills
add-observability
add-persistence
add-rag
add-structured-output
add-token-budgeting
add-tool
cache-llm-calls
define-prompt
domain-model-subtask-pipeline
references
enable-prompt-caching
handle-agent-events
manage-state
migrate-from-0-x
model-planner-subtasks
persist-chat-history
query-sql-from-agent
scaffold-agent
snapshot-and-restore
test-koog-agents
trace-agent-internals
use-attachments
use-functional-agent
use-llm-node-variants
use-planner
wire-a2a
wire-acp-server
wire-ktor-server
wire-mcp-server
wire-spring-boot