Text-to-speech

Convert text to speech with ElevenLabs Eleven v4 Turbo: returns audio (the base64-encoded file in the format asked for: mp3, opus, aac, flac, wav or pcm) with model, voice, format and chars (the characters spoken). Send POST /api/tts with the required field text and pay $0.120 per call over x402 or MPP (there is no free tier). It returns a JSON object with model, provider, voice, format, audio and 1 more.

The ten OpenAI voice names each map to their own ElevenLabs voice, or name one of 21 ElevenLabs voices directly; the answer names the voice that spoke. 90+ languages on ElevenLabs. If ElevenLabs is busy, throttling or down, a backup speech model with fewer voices and languages serves the call and the answer's model field names it. No API key needed; pay per call over x402 or MPP. Text capped at 2000 chars. Model-backed. For high-volume speech where timbre matters less, /api/tts-lite is the same interface on Kokoro-82M at $0.005.

Category: AI & compute · Tags: tts text-to-speech audio voice speech elevenlabs eleven-v4-turbo

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/tts \
  -H "Content-Type: application/json" \
  -d '{"text":"Hello from Agent402!","voice":"alloy","format":"mp3"}'

Without payment this returns HTTP 402 Payment Required with the exact price for tts; any x402 v2 or MPP client pays it and retries.

Example response

{
  "model": "elevenlabs/eleven-v4-turbo",
  "provider": "openrouter",
  "voice": "river",
  "format": "mp3",
  "audio": "<base64-encoded audio>",
  "chars": 20
}

From an MCP client

catalog.call {
  "slug": "tts",
  "params": {
    "text": "Hello from Agent402!",
    "voice": "alloy",
    "format": "mp3"
  }
}

The hosted connector at https://agent402.tools/mcp needs a payment for tts; the stdio package pays it from a wallet or from AGENT402_CREDITS_KEY. Local install: npx -y agent402-mcp.

Errors and behavior

• text is required. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example, so the caller can correct it.
• A paid call that ends in any status of 400 or above is not charged over x402, MPP or a prepaid credits key: settlement is cancelled when the tool fails. The exception is a Tempo push credential, a transfer the buyer sent before the call: it settles before the tool runs, so if the tool then fails the payment is recorded as a refund owed to the paying wallet.
• Wallet-only: this tool runs a model, so it has no proof-of-work tier. A prepaid card-credits key issued earlier (Authorization: Bearer a402_...) also pays it.
• Model-backed: the answer is generated by a model, so the same input can produce different wording.
• A GET or HEAD to /api/tts returns the same 402 quote, so the price can be read without a body.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB is not replayed).

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
client.setSpendControls?.(false); // keep your own spending ceiling in code
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/tts", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "text": "Hello from Agent402!",
    "voice": "alloy",
    "format": "mp3"
  }),
});

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