Knowledge Base
A knowledge base gives your agent access to reference material it can search during conversations. Instead of putting every detail in the prompt, you can upload documents, add URLs, or paste text that the agent retrieves in real time when a caller asks a relevant question.
When to Use a Knowledge Base
Use a knowledge base when your agent needs to reference information that is:
- Too detailed for the prompt — A 50-page FAQ, product catalog, or policy document.
- Frequently changing — Price lists, schedules, or inventory that updates regularly.
- Shared across agents — Multiple agents need the same reference material.
Keep using the prompt for core personality, conversation flow, and essential business rules. The knowledge base is for supplementary reference data.
Think of the prompt as the agent’s training — what it always knows. The knowledge base is like a reference binder it can flip through when asked a specific question.
Creating a Knowledge Base
- Navigate to the agent you want to add a knowledge base to.
- Open the Agent Editor.
- Scroll to the Knowledge Base section.
- Click Create Knowledge Base.
- A knowledge base is created and linked to this agent.
Each agent can have one knowledge base. A knowledge base can contain multiple sources.
Source Types
File Upload
Upload documents directly to the knowledge base. The agent’s voice provider processes and indexes the content for retrieval.
Supported file formats:
- PDF (.pdf)
- Microsoft Word (.docx, .doc)
- Plain text (.txt)
- CSV (.csv)
- Markdown (.md)
- TSV (.tsv)
- JSON (.json)
- XML (.xml)
File size limits:
| Provider | Maximum File Size |
|---|---|
| Retell AI | 50 MB |
| Vapi | 10 MB |
| Bland.ai | 10 MB |
To upload a file:
- Click Add Source in the knowledge base section.
- Select File.
- Choose a file from your computer or drag and drop it.
- The file uploads and processing begins. Status shows as “Processing” until complete.
File processing typically takes 10–60 seconds depending on file size. The agent cannot reference the content until processing is complete and the status shows “Ready”.
URL Source
Provide a web page URL and BuildVoiceAI scrapes its content for the knowledge base. This is useful for existing FAQ pages, product listings, or help center articles.
To add a URL source:
- Click Add Source.
- Select URL.
- Enter the full URL (including
https://). - Click Add. The page content is fetched and processed.
URL scraping captures the text content of the page. It does not follow links to other pages — each URL must be added individually.
Auto-refresh (Retell AI only): URL sources on Retell-powered agents automatically refresh every 12–24 hours, picking up any changes to the web page content. This keeps the knowledge base current without manual intervention.
Text Source
Paste raw text directly into the knowledge base. This is the simplest option for small amounts of structured information like FAQs, product details, or policy snippets.
To add a text source:
- Click Add Source.
- Select Text.
- Enter a title for the text snippet (for your reference).
- Paste or type the content.
- Click Add.
Text sources are processed immediately and available to the agent within seconds.
Provider Differences
Not all source types are available with every voice provider:
| Source Type | Retell AI | Vapi | Bland.ai |
|---|---|---|---|
| File upload | Yes | Yes | Yes |
| URL | Yes | No | Yes |
| Text | Yes | No | Yes |
| Auto-refresh (URL) | Yes (12–24 hrs) | N/A | No |
If you switch an agent’s provider after adding knowledge base sources, some sources may not be compatible with the new provider. Check the table above and re-add sources as needed.
Managing Sources
Viewing Sources
The knowledge base section in the Agent Editor lists all sources with:
- Name/Title — The file name, URL, or text title.
- Type — File, URL, or Text.
- Status — Processing, Ready, or Error.
- Date added — When the source was added.
Deleting Sources
Click the delete icon next to any source to remove it. The agent will no longer be able to reference that content during calls. Deletion takes effect immediately.
Updating Sources
- Files — Delete the old file and upload the new version.
- URLs — Wait for auto-refresh (Retell only) or delete and re-add the URL.
- Text — Delete and re-add with updated content.
Best Practices
Structure your content clearly
Use headings, bullet points, and clear sections in your documents. The AI retrieves relevant chunks of text during calls, so well-structured content produces better results than unformatted blocks of text.
Keep information factual and concise
The knowledge base works best with factual reference material — FAQs, specifications, policies, pricing tables. Avoid narrative or marketing copy that doesn’t contain actionable information.
Test with specific questions
After adding sources, make test calls and ask the agent specific questions that should be answered by the knowledge base. This verifies the content is being retrieved correctly.
Don’t duplicate the prompt
If information is already in the agent’s prompt, don’t also put it in the knowledge base. This can cause conflicting answers. Use the prompt for essential behavior and the knowledge base for extended reference material.
Monitor for accuracy
Periodically review call transcripts to ensure the agent is citing knowledge base information correctly. If you notice inaccuracies, check the source material for errors or ambiguous phrasing.