Rate Limits

Understand API rate limits and concurrency

Rate limits prevent abuse and ensure fair usage for all users.

Concurrency limits

Maximum concurrent requests per plan:

Plan	Regular TTS	Streaming TTS
Pro	18	10
Business	25	15

Requests beyond these limits will queue or be rejected.

Request limits

• Max text length: 5,000 characters per request
• Timeout: 120 seconds (regular), 180 seconds (streaming)

How it works

When you hit the concurrency limit:

1. New requests queue automatically
2. Requests process as slots become available
3. Queued requests timeout after 30 seconds

Handling rate limits

Check your concurrent requests

Track active requests in your application:

let activeRequests = 0;
const MAX_CONCURRENT = 18; // Pro plan

async function throttledRequest(text, voice, model) {
  while (activeRequests >= MAX_CONCURRENT) {
    await new Promise(resolve => setTimeout(resolve, 100));
  }

  activeRequests++;
  try {
    return await makeRequest(text, voice, model);
  } finally {
    activeRequests--;
  }
}

Use a queue

For many requests, use a proper queue:

import PQueue from 'p-queue';

const queue = new PQueue({ concurrency: 18 });

// Add requests to queue
const results = await Promise.all([
  queue.add(() => makeRequest(text1, voice, model)),
  queue.add(() => makeRequest(text2, voice, model)),
  queue.add(() => makeRequest(text3, voice, model))
]);

Split large texts

Keep requests under 5,000 characters:

function splitText(text, maxLength = 5000) {
  const sentences = text.match(/[^.!?]+[.!?]+/g) || [text];
  const chunks = [];
  let current = '';

  for (const sentence of sentences) {
    if ((current + sentence).length > maxLength) {
      chunks.push(current.trim());
      current = sentence;
    } else {
      current += sentence;
    }
  }

  if (current) chunks.push(current.trim());
  return chunks;
}

Monitor usage

Check your balance regularly:

curl https://api.neospeech.io/v1/balance \
  -H "Authorization: Bearer YOUR_API_KEY"

Response shows:

• Total credits
• Used credits
• Remaining credits
• Overage (if any)

Upgrade limits

Need higher limits? Contact support for enterprise plans with:

• Higher concurrency
• Custom rate limits
• Dedicated infrastructure