---

name: retellai-sdk-patterns description: 'Production-ready Retell AI SDK patterns for voice agent applications.

Use when building production voice agents, implementing retry logic, or establishing patterns.

Trigger with phrases like "retell patterns", "voice agent patterns", "retell best practices".

' allowed-tools: Read, Write, Edit version: 1.9.0 license: MIT author: Jeremy Longshore jeremy@intentsolutions.io tags:

• saas
• retellai
• voice
• telephony
• patterns compatibility: Designed for Claude Code

---

Retell AI SDK Patterns

Overview

Production-ready patterns for Retell AI: client singletons, typed agent configurations, call management, and error handling.

Prerequisites

• Completed retellai-install-auth
• retell-sdk installed

Instructions

Step 1: Singleton Client

import Retell from 'retell-sdk';

let _retell: Retell | null = null;

export function getRetellClient(): Retell {
  if (!_retell) {
    _retell = new Retell({ apiKey: process.env.RETELL_API_KEY! });
  }
  return _retell;
}

Step 2: Typed Agent Configuration

interface AgentConfig {
  name: string;
  voiceId: string;
  prompt: string;
  functions?: FunctionConfig[];
  maxCallDurationMs?: number;
  endCallAfterSilenceMs?: number;
}

async function createAgent(config: AgentConfig) {
  const retell = getRetellClient();

  const llm = await retell.llm.create({
    model: 'gpt-4o',
    general_prompt: config.prompt,
    functions: config.functions,
  });

  const agent = await retell.agent.create({
    response_engine: { type: 'retell-llm', llm_id: llm.llm_id },
    voice_id: config.voiceId,
    agent_name: config.name,
    max_call_duration_ms: config.maxCallDurationMs || 300000,
    end_call_after_silence_ms: config.endCallAfterSilenceMs || 10000,
  });

  return { agentId: agent.agent_id, llmId: llm.llm_id };
}

Step 3: Call Manager with Retry

async function makeCallWithRetry(
  fromNumber: string, toNumber: string, agentId: string, maxRetries = 2
) {
  const retell = getRetellClient();
  for (let attempt = 0; attempt <= maxRetries; attempt++) {
    try {
      const call = await retell.call.createPhoneCall({
        from_number: fromNumber,
        to_number: toNumber,
        override_agent_id: agentId,
      });
      return call;
    } catch (err: any) {
      if (attempt === maxRetries || err.status < 500) throw err;
      await new Promise(r => setTimeout(r, 2000 * (attempt + 1)));
    }
  }
}

Step 4: Batch Call Campaign

async function runCallCampaign(
  numbers: string[], agentId: string, concurrency = 3, delayMs = 2000
) {
  const results: Array<{ number: string; callId?: string; error?: string }> = [];
  const queue = [...numbers];
  const active = new Set<Promise<void>>();

  while (queue.length > 0 || active.size > 0) {
    while (active.size < concurrency && queue.length > 0) {
      const number = queue.shift()!;
      const p = (async () => {
        try {
          const call = await makeCallWithRetry(process.env.RETELL_PHONE_NUMBER!, number, agentId);
          results.push({ number, callId: call.call_id });
        } catch (err: any) {
          results.push({ number, error: err.message });
        }
        await new Promise(r => setTimeout(r, delayMs));
      })();
      active.add(p);
      p.finally(() => active.delete(p));
    }
    if (active.size > 0) await Promise.race(active);
  }
  return results;
}

Output

• Singleton Retell client
• Typed agent creation with LLM configuration
• Retry logic for call creation
• Concurrent call campaign manager

Error Handling

| Pattern | Use Case | Benefit | |---------|----------|---------| | Singleton | All SDK calls | One client instance | | Typed config | Agent creation | Type safety, defaults | | Retry wrapper | Call failures | Automatic recovery | | Campaign manager | Outbound calls | Rate-limited concurrency |

Examples

Use an idempotency boundary around call creation

Generate a request identifier at the application edge and persist its state before invoking the Retell SDK. If the network response is lost, retrieve the existing result by that identifier or operator-visible correlation data before attempting another call. Keep retries bounded and limited to operations whose outcome can be established; this prevents a transient client failure from creating multiple customer calls.

Resources

• retell-sdk npm
• Retell AI Documentation

Next Steps

Apply in retellai-core-workflow-a for agent building.