## **In-Brief** - **SSML transforms** robotic text-to-speech into natural, human-sounding voice interactions by giving developers precise control over how computers speak. - **Essential tags** like ``, ``, and `` control speech pace, stress important words, and create natural conversation flow. - **Proper implementation** requires strategic voice selection, thorough testing, and understanding platform limitations to build voice agents users actually want to engage with. Most computer voices sound like they learned English from a tax form. Flat. Robotic. The kind of speech that makes you want to hang up before the automated system finishes its first sentence. ## **What Is SSML?** Speech Synthesis Markup Language fixes this problem. It transforms synthetic speech from mechanical drone into something that actually sounds human. Created by the World Wide Web Consortium, this XML-based markup language gives developers [precise control](https://www.w3.org/TR/speech-synthesis11/) over how computers talk. Think of it this way: instead of handing an actor a script and walking away, you're actually directing their performance. You control the pace, the pauses, the emphasis, even how to pronounce tricky words. Because real humans don't speak like GPS directions. The technology shines when handling multiple languages and pronunciations. If you're building for a global audience, this matters. Vapi's Voice AI platform supports over 100 languages, letting developers create voice applications that sound natural regardless of where users live. Whether you're building a virtual assistant, an IVR system, or making [content more accessible](https://www.w3.org/WAI/WCAG21/Understanding/), proper markup separates engaging voice agents from the ones people actively avoid. ## **Understanding Tags and Syntax** These tags transform computer speech from mechanical to human. Each one serves a specific purpose in creating natural-sounding interactions. ### **Basic Tags** Start with these four essential elements: - **``**: The wrapper that tells the speech engine to interpret your content as markup instead of plain text. - **``**: Creates precisely timed pauses in speech. - **``**: Controls pitch, rate, and volume for natural speech patterns. - **``**: Stresses specific words to guide listener attention. ``` xml ``` ``` Let's take a moment to consider the options. This will be spoken slowly, with a low pitch and loud volume. I really need your help. ``` ### **Advanced Features** Ready for more control? These tags handle complex scenarios: - **``**: Tells the engine how to interpret dates, numbers, and phone numbers correctly. - **``**: Specifies exact pronunciation using phonetic alphabets. - **`_{`**: Provides spoken substitutions for text.
- **`}

Articles

Build your own voice agent.

Articles

How We Solved DTMF Reliability in Voice AI Systems

How We Built Adaptive Background Speech Filtering at Vapi

How we solved latency at Vapi

Three Examples of Voice AI Improving Logistics

Understanding Kindroid: Lessons from the AI Companion Market

What Is RCS Messaging? The Complete Guide for Developers

Introduction to Adobe Podcast Tools for Podcasting

Launching the Vapi for Creators Program

Bring Vapi Voice Agents into Your Workflows With The New Vapi MCP Server

Vapi x Deepgram Aura-2 — The Most Natural TTS for Enterprise Voice AI

Vapi x Cartesia: Ultra-Realistic Voice AI with Sonic 2.0

AI Call Centers are changing Customer Support Industry

Build your own voice agent.

Build your own
voice agent.

Build your own
voice agent.