AI knowledge base for voice agents

Knowledge in. Better answers out.
Retell's AI knowledge base turns your existing content into live context for every call. Add webpages, files and text, or sync Google Drive, OneDrive and Notion. Before each reply, your agent pulls the most relevant passages and answers from them, which keeps answers tied to your own policies and reduces hallucinations.
Overview

Move beyond prompt-only AI

An AI knowledge base is a collection of your own content that an AI agent searches during a conversation and uses as context for its reply. Prompts are hard to maintain and easy to outgrow. A knowledge base lets your agent draw on policies, catalogs and help articles that would never fit in a prompt, and you update the content without rewriting the agent.

Webpages and sites
Key Points
Supports single pages or entire websites
Retrieval generally adds under 100 ms
Auto-crawl a URL path and refresh every 24 hours
Up to 500 URLs per knowledge base
Files
Key Points
PDF, DOCX, Markdown, CSV, XLSX, PPTX and more
Up to 25 files per knowledge base, 50 MB each
Well-structured Markdown retrieves more accurately
Text and connected apps
Key Points
Up to 50 text snippets per knowledge base
Sync Google Drive, OneDrive and Notion
Changed sources re-sync on the daily auto-refresh
Feature

Feed your agent the content it needs to answer with confidence

When you create a knowledge base, Retell splits each source into chunks, embeds them and stores them in a vector database. During a call, before each reply, it condenses the recent conversation into a short search query, pulls the closest chunks (3 by default) and adds them to the LLM prompt. No prompt changes are needed, and an agent can use more than one knowledge base.

Retell dashboard Knowledge Base tab showing a knowledge base of five uploaded documentation files, with the workspace's other knowledge bases listed beside it.
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How It Works

How to use a knowledge base, step by step

Retell dashboard Knowledge Base tab with a knowledge base of website and file sources.
Create it
Open the Knowledge Base tab and select Add. Then pick a source:
URL: import a page, or crawl every page under a URL path
File: upload PDF, DOCX, Markdown, spreadsheets and more
Text: paste content directly
Google Drive, OneDrive or Notion: sync from a connected account
 
Retell agent editor with the Knowledge Base settings section.
Add it
In the agent editor, open Knowledge base & memory, select Add and choose your knowledge bases. Advanced settings set how many chunks to retrieve and how strict matching is.
 
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Retell agent editor with a knowledge base attached to the agent.
Test it
Ask a related question in the test panel. The agent searches the knowledge base on its own, with no prompt changes. After a call, open its transcript in Call History to see exactly which chunks were retrieved.
 
Product Highlights

Built to Handle
the Real World

Answers stay current.
Auto-refresh re-fetches your URLs and re-syncs changed Google Drive, OneDrive and Notion sources every 24 hours. If a source can't be refreshed, its existing content is kept.
One source for voice and chat.
Chat agents use the same knowledge bases as voice agents, so callers and website visitors get answers from the same content.
See what the agent retrieved.
Every agent turn that used the knowledge base shows a Knowledge Base Retrieval link in Call History, with the exact chunks passed to the LLM.
Tune retrieval, not just prompts.
Set chunks to retrieve and a similarity threshold, add a Knowledge Base Instruction to focus the search, or attach a knowledge base to a single node in a conversation flow.
Use Cases

Proven Impact Across 

Industries

Explore Retell Customers
Inbounds
Inbounds.com has scaled and optimized its call campaigns without sacrificing the human oversight essential to its customers' success.
“Our early adoption of Retell AI, combined with our ability to deeply customize it and build our own infrastructure around it, really gives us an edge in the industry.”
Leonardo Danconia
CEO and Cofounder, inbounds.com
Swtch Energy
The cost of our customer support team was increasing 300 to 400 percent a year. By introducing Retell and building Lucas, we were able to reduce that burden by over 50 percent, drastically improve our SaaS margins, and still support our customers during high-growth and urgent situations.
Carter Li
CEO
Matic Insurance
As we’ve explored ways to drive greater efficiency in our business over the past 18 to 24 months, leveraging AI technologies has become a key part of that strategy. By doing so, we’re able to reduce the cost of acquiring new customers, and at the same time, maintain, or even lower, the cost of retaining and servicing them throughout their lifecycle with us.
Brian Barker
Product Manager
Integrations

Seamless

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  • Avaya
  • Genesys
  • Five9
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  • Telnyx
  • Make
  • Cal.com
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Features

Explore how Retell AI can transform every part of your call operations. See the full range of capabilities designed for smarter automation, better efficiency, and enhanced customer experience.

Competitor overview

What an AI knowledge base does on a live call

An AI knowledge base is a collection of your own content, such as webpages, documents and text, that an AI agent searches during a conversation and uses as context for its reply. On a phone call that search has to fit between the caller finishing a sentence and the agent starting to speak, so Retell runs it before every response the agent gives.

Diagram of how a Retell AI knowledge base feeds a voice agent. Before the call, webpages (up to 500 URLs), files (50 MB each), text snippets (up to 50) and synced Google Drive, OneDrive and Notion content are split into chunks, embedded and stored in a vector database, linked to agents and auto-refreshed every 24 hours when enabled. During the call, before every reply: 1 the caller speaks, 2 the recent conversation is condensed into a search query, 3 the closest chunks are retrieved (3 by default, similarity threshold 0.6), 4 they are added to the LLM prompt under Related Knowledge Base Contexts, 5 the agent answers. Retrieval generally adds under 100 ms.
How a Retell AI knowledge base is built before the call and searched before every agent reply. Diagram by Retell AI, October 2026. Source: Retell knowledge base docs.

You don't need to change your prompt. Once a knowledge base is linked to an agent, it is searched automatically, and the retrieved text is added to the LLM prompt before the agent replies. Keep facts in the knowledge base and keep instructions in the agent's prompt.

What you can add to a Retell knowledge base

Source What it holds How it stays current Limit per knowledge base
URLs Single pages, or every page under a URL path with auto-crawl Auto-refresh and auto-crawl every 24 hours, when enabled 500 URLs
Files PDF, DOCX, Markdown, TXT, HTML, CSV, XLSX, PPTX and more Re-upload when the file changes 25 files, 50 MB each; spreadsheets up to 1,000 rows and 50 columns
Text Snippets you paste or type in the dashboard Edit in the dashboard 50 snippets
Google Drive, OneDrive, Notion Docs, Sheets, files and pages from a connected account Changed sources re-sync on the 24 hour auto-refresh, when enabled See the sync guides

Need more room? Create another knowledge base. An agent can use more than one, and chat agents use the same knowledge bases as voice agents.

Retrieval is only as good as the source. Retell's docs recommend Markdown with clear headings, short sections and specific names, dates and units, because each chunk is read on its own. Our guide on how to structure a voice AI knowledge base goes further, and what grounding in AI means covers why answers from your own content are more reliable than answers from training data alone.

AI knowledge base FAQ

What is an AI knowledge base?

An AI knowledge base is a collection of your own content, such as webpages, documents and text, that an AI agent searches during a conversation and uses as context for its answer. In Retell, sources are split into chunks and stored in a vector database, and the agent retrieves the most relevant chunks before each reply.

Do I need to change my agent's prompt to use a knowledge base?

No. Once a knowledge base is linked to an agent, Retell searches it automatically before every response. You don't need to mention it in the prompt.

How do I stop the agent from answering outside the knowledge base?

Add an instruction to the agent's prompt telling it to answer only from the retrieved knowledge base context, which appears under the heading Related Knowledge Base Contexts, and to say so when no related information is found. Retell's knowledge base docs include a sample instruction you can copy.

Does the knowledge base add latency to calls?

Retell has optimized knowledge base retrieval for real-time calls, and it should generally add under 100 ms of latency.

How much does the Retell knowledge base cost?

Your first 10 knowledge bases are free, and each additional one is $8 per month. Calls with a knowledge base enabled cost an extra $0.005 per minute, whether the agent uses one knowledge base or several. Voice agents start from $0.07 per minute.

How does the knowledge base stay up to date?

Turn on auto-refresh and Retell re-fetches your URLs and re-syncs changed Google Drive, OneDrive and Notion sources every 24 hours. If a source can't be refreshed, its existing content is kept. Uploaded files don't sync, so re-upload a file after it changes.

Can chat agents use the same knowledge base as voice agents?

Yes. Chat agents use the same knowledge bases as voice agents, so a caller and someone chatting on your website or over SMS get answers from the same content.

How can I see which content the agent used on a call?

Open the call in Call History. Every agent turn that used the knowledge base shows a Knowledge Base Retrieval link that lists the exact chunks passed to the LLM for that response.

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