Builder API Reference

Agent objective

Produce a complete, correctly-ordered builder chain with the right .withX() calls for the task. Every method used must exist in this reference.

When to load this skill

• Before writing any agent builder chain
• When unsure which methods are available or what their params are
• When upgrading from an older API version

Two syntaxes, one API

The declarative createAgent(config) front door and this fluent builder are the same API — same key names, same nesting (createAgent({ tools: { allowedTools } }) ≡ .withTools({ allowedTools })). Use createAgent for static definitions; the builder for conditional/imperative construction or code-only escape hatches (.withHook, .withLayers, .compose). This reference lists the fluent methods; each maps to an AgentConfig key of the same name.

import { createAgent } from "@reactive-agents/runtime";

const agent = await createAgent({
  name: "assistant",
  provider: "anthropic",
  reasoning: { defaultStrategy: "adaptive", maxIterations: 10 },
});

Implementation baseline

import { ReactiveAgents } from "@reactive-agents/runtime";

// Minimal — provider + reasoning is enough to run
const agent = await ReactiveAgents.create()
  .withName("assistant")
  .withProvider("anthropic")
  .withReasoning({ defaultStrategy: "adaptive", maxIterations: 10 })
  .build();

// Production — adds reliability, observability, cost controls
const agent = await ReactiveAgents.create()
  .withName("assistant")
  .withProvider("anthropic")
  .withModel("claude-opus-4-6")
  .withReasoning({ defaultStrategy: "adaptive", maxIterations: 15 })
  .withTools({ allowedTools: ["web-search", "file-read", "checkpoint"] })
  .withMemory({ tier: "enhanced", dbPath: "./agent.db" })
  .withGuardrails({ injection: true, pii: true, toxicity: true })
  .withVerification()
  .withCostTracking({ perRequest: 0.50, daily: 20.0 })
  .withObservability({ verbosity: "normal", live: true })
  .withMaxIterations(20)
  .build();

Full builder API reference

Identity & persona

Method	Params	Notes
.withName(name)	string	Display name; defaults to "agent"
.withAgentId(id)	string	Override auto-generated ID
.withPersona(p)	{ role?, background?, instructions?, tone? }	Generates system prompt from fields
.withSystemPrompt(s)	string	Raw system prompt — overwrites .withPersona()
.withEnvironment(ctx)	Record<string, string>	Key-value pairs injected into system prompt

Provider & model

Method	Params	Notes
.withProvider(p)	"anthropic"|"openai"|"gemini"|"ollama"|"litellm"|"test"	Required
.withModel(m)	string | { model, thinking?, temperature? }	Uses provider default if omitted
.withRateLimiting(cfg)	{ requestsPerMinute?, tokensPerMinute?, maxConcurrent? }	Provider-level rate limits
.withCircuitBreaker(cfg?)	{ failureThreshold?, cooldownMs?, halfOpenRequests? }	Retries with backoff on errors
.withDynamicPricing(provider)	PricingProvider	Fetches live pricing during build
.withModelPricing(registry)	Record<string, { input, output }>	Custom per-model USD pricing

Reasoning & iteration

Method	Params	Notes
.withReasoning(opts?)	{ defaultStrategy?, maxIterations?, enableStrategySwitching?, maxStrategySwitches?, fallbackStrategy? }	Strategies: "reactive", "plan-execute-reflect", "tree-of-thought", "reflexion", "adaptive"
.withMaxIterations(n)	number	Hard cap; overrides .withReasoning value
.withRequiredTools(cfg)	{ tools?, adaptive?, maxRetries? }	Forces tool calls before completion

Tools

Method	Params	Notes
.withTools(opts?)	{ tools?, allowedTools?, adaptive?, resultCompression? }	No args = all built-ins enabled
.withDocuments(docs)	DocumentSpec[]	RAG context injection
.withPrompts(opts?)	prompts config	Custom prompt templates

Memory

Method	Params	Notes
.withMemory(opts?)	"standard" | "enhanced" | { tier, dbPath?, capacity? }	"enhanced" requires writable SQLite path

Safety & compliance

Method	Params	Notes
.withGuardrails(opts?)	{ injection?, pii?, toxicity?, customBlocklist? }	All default true
.withKillSwitch()	—	Exposes .pause(), .resume(), .stop(), .terminate()
.withBehavioralContracts(c)	{ deniedTools?, allowedTools?, maxToolCalls?, maxIterations?, maxOutputLength?, deniedTopics?, requireDisclosure? }	Rule-based constraints
.withVerification(opts?)	{ semanticEntropy?, factDecomposition?, nli?, hallucinationDetection?, passThreshold?, useLLMTier? }	Runtime hallucination detection
.withAudit()	—	Append-only action audit log

Cost

Method	Params	Notes
.withCostTracking(opts?)	{ perRequest?, perSession?, daily?, monthly? }	USD budgets; throws on breach

Observability & logging

Method	Params	Notes
.withObservability(opts?)	{ verbosity?, live?, logModelIO?, file?, telemetry?, tracing? }	file is JSONL output path; telemetry: true | { mode: "contribute"|"isolated" } enables run telemetry
.withLogging(cfg)	{ level?, format?, output?, filePath?, maxFileSizeBytes?, maxFiles? }	Structured logging

Persistence & integration

Method	Params	Notes
.withGateway(opts?)	GatewayOptions	Persistent agent with heartbeats/crons/webhooks
.withA2A(opts?)	{ port?, basePath? }	A2A server (JSON-RPC 2.0 + SSE)
.withStreaming(opts?)	{ density?: "tokens"|"full" }	Streaming output
.withAgentTool(name, cfg)	name + { agent }	Local agent registered as a tool
.withDynamicSubAgents(opts?)	{ maxIterations? }	Dynamic sub-agent spawning
.withRemoteAgent(name, url)	name + A2A URL	Remote A2A agent as callable tool
.withCortex(url?)	optional URL	Cortex desk server integration
.withHealthCheck()	—	Self-monitoring health endpoint
.withErrorHandler(fn)	(err, ctx) => void	Custom error handling callback
.withHook(hook)	LifecycleHook	Lifecycle callbacks (beforeRun, afterStep, etc.)
.withSelfImprovement()	—	Meta-learning from past runs
.withExperienceLearning()	—	Injects prior-run experience tips into context

Build

Method	Returns	Notes
.build()	Promise<ReactiveAgent>	Always await
.buildEffect()	Effect<ReactiveAgent>	For Effect runtime callers
ReactiveAgents.fromConfig(cfg)	Promise<ReactiveAgentBuilder>	From AgentConfig object
ReactiveAgents.fromJSON(json)	Promise<ReactiveAgentBuilder>	From JSON string
ReactiveAgents.runOnce(task, builder)	Promise<AgentResult>	Build + run + dispose

Pitfalls

• .build() is async — always await or you get an unresolved Promise
• .withPersona() and .withSystemPrompt() both set the system prompt — the last call wins
• .withTools() no-args enables 5 standard tools: web-search, http-get, file-read, file-write, code-execute — shell-execute is opt-in only via .withTools({ terminal: true }) (see shell-execution-sandbox skill)
• .withTools({ terminal: true }) enables shell execution sandboxed via Docker or local allowlist — use with caution in production
• .withMemory("enhanced") without dbPath uses a default path — set it explicitly in multi-agent environments to avoid collisions
• .withGateway() requires calling .start() on the built agent; .build() alone does not start the loop
• enableStrategySwitching: true without maxStrategySwitches defaults to 2 switches max