Vapi vs Retell AI: which voice platform suits your website?

How do Vapi and Retell AI compare?

Both build voice agents for phone and web, with a widget, a Web SDK, an API and an MCP server. They differ in how they charge, what their widgets offer and where knowledge comes from. We checked both on their official pages on 8 October 2026.

How do the Vapi and Retell AI web widgets work?

Vapi’s web widget adds “a complete AI chat and voice interface” with a single line of code. You choose voice or chat mode, a light or dark theme and one of four corners, and you can ask for consent before first use. It needs a public API key and an assistant ID, and Vapi says to restrict that key to the origins and assistants that need it.

Retell AI’s widget is a script tag with a public key limited to your domains. With a voice agent, visitors talk over WebRTC; add a chat agent and they can switch between voice and chat. A callback mode collects a phone number and has your agent ring the visitor, and optional reCAPTCHA v3 adds bot protection.

Both also have a Web SDK for building your own call screen. Kawl Now’s widget is voice only: visitors type what they need, allow the microphone and talk, with live captions, mute and an end button, after a notice that they are speaking with AI and that a transcript is saved.

How does each one handle a knowledge base?

Vapi builds its knowledge base from uploaded files such as .txt, .pdf, .docx, .csv or .md. You select files for an assistant and publish, and Vapi creates a query tool that searches them during calls. Developers can connect their own retrieval server instead.

Retell AI takes documents too, plus web pages, text and files synced from Google Drive, OneDrive or Notion. Optional auto-refresh re-fetches sources every 24 hours, auto-crawl adds new pages under a path, and call history shows the chunks behind each answer. Using a knowledge base adds $0.005 a minute.

Kawl Now adds a review step. Support uses FAQs, notes and selected GitHub .md, .mdx or .txt files, sales has its own notes, and every new or re-synced source waits for approval before callers hear it.

How much setup do Vapi and Retell AI need?

In Vapi, you start blank or from a template such as Customer Support, choose a model preset or your own transcriber, model and voice, and write the first message and system prompt. Composer, an AI builder still in alpha, can also create an assistant from a plain-English description. Squads link several assistants, and simulations test them before customers call.

In Retell AI, you pick a single prompt or a visual conversation flow, then start from scratch, from a template or from a description that Conductor, its AI copilot, turns into a draft. Test calls in the dashboard run in the browser for free.

Kawl Now starts each workspace with a support agent and a sales agent, both switched off. You approve knowledge, set a greeting and voice, add your site’s address and test in the dashboard before you switch on customer calls.

How do Vapi and Retell AI charge for calls?

Vapi passes provider costs through: $0.05 a minute for hosting, with speech-to-text, the model, the voice and transport at each provider’s listed price. With Deepgram, OpenAI and ElevenLabs, its calculator estimated $82 to $129 a month for 1,000 minutes. Usage-only billing includes four concurrent calls, and Success Packages start at $29 a month.

Retell AI sets its own rate for each part, including $0.055 a minute for voice infrastructure, and lists $0.07 to $0.31 a minute for voice agents. Twenty concurrent calls are included, and calls are billed to the second.

On both, longer prompts and longer calls cost more. Kawl Now counts conversations instead, and paid calls aren’t available yet, so no payment is collected.

Which one is more focused on phone calls?

Both lead with the phone, and both offer batch outbound calling and IVR navigation. Retell AI describes itself as an AI voice agent platform for phone calls, its quick start builds a phone agent, and it also sells branded caller ID and verified numbers for US outbound calls.

Vapi calls itself the developer platform for voice agents that make and receive phone calls. Its free US numbers take inbound calls only, so outbound calls use a number imported from Twilio, Telnyx, DIDWW or a SIP trunk.

If your customers need to ring a number, choose either platform over Kawl Now, which has no phone number.

When is Kawl Now the simpler choice?

Kawl Now suits a SaaS team that wants voice answers on its own website without building on a developer platform. It has no phone number for customers to call and no CRM connections, greets callers in English in one of two voices, and offers human handover to your team only as an early release, with customer routing still being tested. If that fits, it gives you:

• Ready-made support and sales agents, each with its own knowledge, greeting, voice and widget.
• Agents that search only sources your team has approved, with GitHub docs reviewed again after each sync.
• An MCP server and REST API for coding agents, where adding a source never approves it.
• Your first 50 conversations free, tests included, with no card.

Common questions