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.
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.
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
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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