API Reference

Use this page when you already understand the concepts and need the current public surface at a glance.

Runnables

API	Use
Runnable<I, O>	base contract with invoke and pipe
RunnableLambda<I, O>	wrap sync or async custom logic
RunnableSequence<I, O>	run steps in order
RunnableParallel<I, TMap>	run branches from the same input concurrently
RunnableMap<I, TMap>	build a named object from one input
RunnablePassthrough<T>	return input unchanged
ModelRunnable	adapt Model into a string -> string runnable

Prompts

PromptTemplate<TVars>

• input: object of template variables
• output: formatted prompt string
• throws: PromptTemplateError when required variables are missing

Output Parsers

API	Behavior
StringOutputParser	returns raw text unchanged
JsonOutputParser<T>	parses JSON text into typed output

JsonOutputParser<T> throws OutputParserError on invalid JSON.

Agent Runtime

Agent

new Agent({ model, tools, passes?, hooks?, maxSteps? })
agent.run(input: string): Promise<string>

Runtime behavior:

• iterative model loop
• tool execution when requested
• memory context injection
• max-step enforcement

Config details:

• tools are registered by unique tool name
• passes can transform interpreted instructions before execution
• hooks.onStart(state) and hooks.onEnd(state, result) allow lifecycle instrumentation
• maxSteps defaults to 20
• runtimePolicy config:
  • modelTimeoutMs: max time for a model call
  • modelRetry.maxAttempts: number of model attempts (default 1)
  • modelRetry.backoffMs: linear backoff base between retries

Tools

tool(...)

tool({
  name,
  description,
  schema,      // zod schema
  execute      // async handler
})

Behavior:

• args are validated against schema before execution
• unknown tool names raise ToolNotFoundError
• schema mismatch raises ToolValidationError

Workflows

Workflow

new Workflow({ steps })
workflow.run(input, { resumeFrom? })

Types:

• WorkflowStep: { id, run, when? }
• WorkflowSnapshot: captured per-step input/output metadata
• WorkflowResumeState: replayable state with nextStepIndex, data, snapshots
• WorkflowRunResult: { output, snapshots, resumeState }

Errors

• ToolNotFoundError
• ToolValidationError
• ModelError
• MaxStepsExceededError
• PromptTemplateError
• OutputParserError

Canonical code mapping and compatibility policy: error-codes.md Versioned runtime contract: core-contract-v0.1.md