# What is a source of truth? > A source of truth is the one trusted place a fact lives, like your price list. Why AI replies need one, and how to hand ChatGPT the facts it may promise. Source: https://learn.ynteractive.com/content/glossary/source-of-truth · Updated 2026-10-01 · Free from Stepthrough (https://learn.ynteractive.com) [Business](https://learn.ynteractive.com/content/glossary#topic-business) · [AI glossary](https://learn.ynteractive.com/content/glossary) Updated October 1, 2026 · By [Robert Breen](https://learn.ynteractive.com/content/about) A source of truth is the one place your business treats as correct for a given fact: the current price list, the booking calendar, the policy document. When two places disagree, the source of truth wins. For AI, it is the set of facts you hand the assistant and tell it not to go beyond. ## Why it matters for a small business Small businesses collect copies of the same facts: a price in an old email, another on the website, a third in someone's head. People cope with that; AI doesn't. If you don't hand the assistant the facts, it fills the gap with something plausible, and a plausible wrong price in a customer email is worse than no answer. A clear source of truth gives it something solid to stand on. It also makes checking possible. If the AI may only promise what is in your facts list, you can compare every line of its draft against that list. Without one, you're just judging whether it sounds right. Keep the facts in one maintained place, then paste or load them from there each time. ## In a real lesson: Reply Faster: Turn a Messy Customer Email Thread into a Clear, Friendly Reply In the [Reply Faster: Customer Emails lesson](https://learn.ynteractive.com/content/chatgpt-reply-to-customer-emails), you answer Dana's messy cake-order thread for Cedar Lane Bakery, a made-up neighborhood bakery. Along with the thread, you paste a numbered list headed "Facts (only promise what is here):" covering the Saturday Oct 3 pickup at 10 a.m., lemon at the same $120 price, the "Happy 40th, Mike!" writing, the allergy answer, the 10% discount and how to sign off. The voice-over explains why: ChatGPT can't know your schedule, your prices or what your kitchen can promise, so you spell them out and number them to check later. That list is the source of truth for this reply. It pays off right away. The first draft says the cake is completely nut-free, which isn't in the facts. You ask ChatGPT for a table of every promise and the fact behind it, it flags the allergy line, and the final reply says honestly that the kitchen also bakes with nuts. The [AI Email Responder](https://learn.ynteractive.com/content/ai-email-responder-gmail-drafts-n8n) does the same inside n8n, with a "What you know" section listing Greenline's service areas, prices and hours. [Try this lesson free](https://learn.ynteractive.com/modules/chatgpt-reply-faster) or [read the step-by-step guide](https://learn.ynteractive.com/content/chatgpt-reply-to-customer-emails). ## Common confusions ### Source of truth vs grounding The source of truth is where the facts live and who keeps them current. [Grounding](https://learn.ynteractive.com/content/glossary/grounding) is giving those facts to the AI so its answer is based on them. ### Source of truth vs knowledge base A [knowledge base](https://learn.ynteractive.com/content/glossary/knowledge-base) is a collection of documents an AI can search. It's only a source of truth if someone owns it and keeps it correct. ## Tips - Keep prices, hours and policies in one document and update that one first. - Number the facts you paste so you can check each claim against them. - Tell the AI what to say when the facts don't cover a question. ## Related terms [Grounding](https://learn.ynteractive.com/content/glossary/grounding) · [Hallucination](https://learn.ynteractive.com/content/glossary/hallucination) · [Self-check prompt](https://learn.ynteractive.com/content/glossary/self-verification) · [Prompt constraints](https://learn.ynteractive.com/content/glossary/prompt-constraints) · [Knowledge base](https://learn.ynteractive.com/content/glossary/knowledge-base) · [System prompt (system message)](https://learn.ynteractive.com/content/glossary/system-prompt) ## Where you use it: free lessons - [Reply Faster: Turn a Messy Customer Email Thread into a Clear, Friendly Reply](https://learn.ynteractive.com/content/chatgpt-reply-to-customer-emails) (ChatGPT, 9 min) - [AI Email Responder: Draft Gmail Replies Automatically with n8n](https://learn.ynteractive.com/content/ai-email-responder-gmail-drafts-n8n) (n8n, 12 min) - [Reply Faster to Clients Chasing Their Refund: ChatGPT for Tax and Bookkeeping Firms](https://learn.ynteractive.com/content/chatgpt-reply-client-refund-emails-accounting) (ChatGPT, 10 min) ## Frequently asked questions **How do I stop ChatGPT from making up prices?** Paste the real prices and policies with the request, tell it to promise only what is in that list, then ask it to check its draft against the list before you send. **Can a Google Sheet be a source of truth?** Yes, if your team agrees it's the correct version and keeps it updated. An automation can read it so AI replies always use the current figures. [All AI glossary terms, A to Z](https://learn.ynteractive.com/content/glossary) · [Free prompt templates](https://learn.ynteractive.com/content/prompts)