AI second brain apps that answer questions only from your notes

AI second brain apps that answer questions only from your notes are rarer than the phrase suggests, and the difference shows in each product's own documentation. Barside's Ask library tells the AI to answer only from passages of your library, and the answer cites them by number. Google says chat responses in NotebookLM, now called Gemini Notebook, “only use data from your sources”, with citations. Obsidian Copilot and Tana describe web tools that can work next to your notes. Mem searches your whole workspace by default, and the two Mem pages we read say nothing about citations or the web.

Everything about the other four products comes from their own documentation, help pages and product pages, as we read them in October 2026. We ran no tests on them, so treat each line as the vendor's statement and open the linked page before you rely on it. We make Barside, a free desktop app for Windows, Linux and Mac, and it gets the same treatment here, limits included.

Which AI second brain apps answer questions only from your notes?

Of the five AI second brain apps compared here, two describe answering questions from your notes and the other sources you chose, with citations: Barside and NotebookLM. Barside's guide says the AI is told to answer only from passages of your library, and Google's chat help page says “Chat responses in Gemini Notebook only use data from your sources.” Obsidian Copilot and Tana document web tools that can work next to your notes, and the two Mem pages we read do not say either way. Three things separate the five: what an answer may draw on, whether it cites the note, and whether the web can join in.

Two names need a word. Google renamed NotebookLM to Gemini Notebook in July 2026, so both names appear in this guide. Obsidian Copilot is the plugin whose documentation calls it Copilot for Obsidian, and Tana's documentation calls its product Tana Outliner.

Do Obsidian Copilot, NotebookLM, Mem and Tana keep the internet out of an answer?

If you want an AI second brain app that answers questions only from your notes, with no internet results mixed in, the pages of Obsidian Copilot, NotebookLM, Mem and Tana say different things. Google says chat responses in NotebookLM, now Gemini Notebook, only use data from your sources, and Tana's docs say its chat models search the web. Copilot leaves it to your setup, and the two Mem pages we read are silent on it.

NotebookLM. Google's announcement of July 16, 2026 says “We're renaming NotebookLM to Gemini Notebook.” The Gemini Notebook product page says it “uses your uploaded sources to answer questions and fulfill requests, providing citations for verification”. A Google Workspace admin help page describes chat as a way to get “grounded information based on your sources”, with “clear inline citations”.

Web pages can be sources too: the product page lists web URLs among the source types, and the admin page says you can upload sources “or discover new sources”. Google's chat help page states the rule in one line: “Chat responses in Gemini Notebook only use data from your sources.” It says the product uses “direct quotes, text, and images from your sources as citations”, and that a more creative request may get the reply “Gemini Notebook can’t answer this question”. The same page describes more chat features, which it calls “experimental and in early development”. They can be used “with or without sources”, and their actions include “searching the web”, so check which chat features you use before you treat a notebook as a closed set.

Obsidian Copilot. The Agent Chat page calls Agent Chat “the default Copilot experience on desktop”, and the documentation home says the agents opencode, Claude Code or Codex can read your vault and use tools, with your approval. The Agent Chat page says Copilot's own web search, web fetch and PDF reading Skills “start turned off in new installs, so agents use their own web and PDF tools”. It also describes your vault as “the agent’s working directory, not a security sandbox”, so a notes-only answer depends on the agent you pick and the tools you allow it. Copilot's lighter Quick Chat works differently: its page says “Chat (free) answers from the context you attach” and that it “does not search your vault automatically”.

Copilot's search page says “Copilot V4 uses ordinary file tools for exact text and file lookup” and offers a service called Miyo for search by meaning. It calls the search scope “a retrieval preference, not a security boundary”, which is a candid thing for a vendor to document.

Mem. Mem's Chat help article says “By default, Mem will search across your entire workspace”, and that you can point Chat at notes or collections you select. Its Chat feature page adds that Mem “reads all relevant notes and gives you a real answer”. Neither page says whether an answer cites the notes it used, and neither mentions web search. From those two pages alone, we can't tell you how Mem treats a question your notes don't cover.

Tana. Tana's AI chat documentation is direct about the web. Under the heading “All models support web search”, it says that when you ask about things not related to your notes, “the models will now search the internet to find the information”, and that they “may include citation links back to the sources used”. The model selector section of the same page says “Some models support web search and reasoning”, marked by icons, so check the model you choose.

In Tana, notes join a chat only when you add them: the AI “provides responses without using your notes unless explicitly added to the chat”, and a note in the docs says “You cannot chat with your whole graph yet”. We found no setting on that page that turns web search off.

How does Barside keep an answer inside your library?

In Barside, the closed set is your library, and an answer takes two steps. First, Barside searches your included notes on your computer and keeps the six best matching passages, with at most two from any one note or bookmark. Then it sends your question and those passages, and nothing else from your library, to the AI you connected. The AI is told to answer only from them and to cite each factual sentence with its source number.

Barside checks the answer before you see it. A citation that points to no real source, or an answer with no citations at all, is set aside, and you see “I could not produce a reliably cited answer” above the closest excerpts so you can read them yourself. If your library does not hold the answer, the reply says what is missing instead of guessing.

To try it with your own notes:

1. Download Barside and bring your notes in. Open Settings & backups, choose Import next to Import notes, then pick Obsidian, Notion, Evernote or files, and you see a preview first. The import guide covers each source, and there is a separate walkthrough for moving an Obsidian vault and keeping its links.
2. Open Settings → AI and connect Claude, ChatGPT, Gemini or OpenRouter. Barside has no AI of its own, so that company writes the answer and bills you for what you use.
3. Open Library & briefing and go to the Sources tab. Under Choose included workspaces & notes, untick any workspace or note you want kept out of answers.
4. On the Ask library tab, type your question in Ask your entire library and press Ask library.
5. Read the answer under From your library. Each source card shows its number, its kind, its workspace and the excerpt the answer used. Click a source's title to open the note.

Keep one thing in mind about the word “notes”. In Barside the closed set is your whole library, and a library can hold web material you put there: articles you saved to Reading, page text you saved for a bookmark, and pages the research agent read. They are things you chose to keep, and unticking a workspace or a note in Sources leaves them out. The guide to AI search that cites its sources lists every kind of source.

Example questions to try, and what to look for in the reply

The sample questions below are examples we wrote for this guide. We did not run them through any of the five apps, so nothing here reports how an app replied. Use them as a pattern and swap in names and topics from your own notes.

Take a made-up researcher, Lena, who keeps two years of customer interview notes and call transcripts in one app. Three example questions would tell her most of what she needs to know about any tool she tries.

• Example question 1, where one note holds the answer: “What did the March interviews say about onboarding?” Look for a short answer, a citation on each factual sentence, and a source that opens at the passage.
• Example question 2, where the answer is spread over several notes: “Which customers asked for an export button, and when?” Look for a citation on each claim. One citation under a long paragraph is a reason to open the notes yourself.
• Example question 3, which the notes cannot answer: “What did we decide about pricing in the April call?”, asked when no April call was ever written down. A good reply says the notes do not cover it. A confident answer with no source is the warning sign, and so is a link to a website she never saved.

Across all three, check four things in the reply:

• A citation you can open. It should lead to the note, and ideally to the passage.
• A plain statement when the notes fall short. The vendors document different things for example 3. Barside's guide says the reply states what is missing, or you see “I could not produce a reliably cited answer” above the closest excerpts. Tana's docs say a question not related to your notes sends the models to the internet. Google's chat help page says chat responses only use data from your sources, and that a more creative request may get “Gemini Notebook can’t answer this question”. We found no statement on this in the Copilot and Mem pages we link.
• No surprise sources. If a reply cites a website, find out whether it is a page you saved or the result of a live search.
• A claim that matches the passage. Open the source before you quote it, because an AI can misread or overstate a passage even when the citation is real.

In Barside, phrase a question with words your notes contain. Its search matches words rather than meaning, so “invoice” will not find a note that only says “bill”. When a first answer misses, ask again with the name of the client, project or person.

Can a notes app run RAG on a personal knowledge base privately, with no internet search?

An AI note-taking app can run RAG on a personal knowledge base privately and with no internet search, but those are two separate promises, and an app can make one without the other. RAG is short for retrieval-augmented generation: the app first retrieves passages from your notes, then a language model writes an answer from them. “No internet search” describes what the answer may draw on. “Private” describes where your passages travel while the answer is written.

• Barside runs the retrieval step on your computer, with no model, no download and no index to build, and Ask library has no web search step. The writing step leaves your computer: your question and the matching excerpts go to the AI company you connected, which is Anthropic, OpenAI, Google or OpenRouter, and that company's data policy applies. The search works offline, and the written answer needs a connection.
• Obsidian Copilot is the one product of the five whose pages, as we read them, describe a model server on your own computer. Its Model Sources and BYOK page says you can choose Ollama or LM Studio “to use their local OpenAI-compatible servers”, and adds: “This does not require a Self-Host license.” The same page says Copilot-hosted models “are cloud services, not local models”, so the model source you choose decides what leaves your computer.
• NotebookLM, Mem and Tana. On the pages we link, we found no mention of running a model on your own computer or of answering without a connection. Google's product page does say “Gemini Notebook never trains models on your uploaded data.” Tana's docs say AI chat “uses AI credits from your plan”, and Mem's help article says “Mem Chat is powered by multiple leading language models.”

If confidentiality is the reason you are searching, our guide to what data goes to the AI provider goes through it feature by feature, and AI notes apps where you bring your own key explains the account side.

Which is the best AI second brain app for answers from only your own notes?

The best AI second brain app for answering questions using only your own notes depends on where those notes live and how strict the limit has to be. Going by what each vendor documents, the choice looks like this:

• You work from a set of documents, web pages and recordings you add to a notebook. Google says chat responses in NotebookLM, now Gemini Notebook, only use data from your sources, with inline citations. Its product page lists Google Docs, PDFs, web URLs, public YouTube video URLs and audio files among the source types.
• Your notes, saved articles and call transcripts live on your computer. Barside's Ask library answers from six passages of your own library, cites its sources by number, and sets aside an answer that comes back without citations. It runs on Windows, Linux and Mac.
• You already work in an Obsidian vault and want a local model. Copilot documents local servers through Ollama and LM Studio, and search by meaning through Miyo. Expect to choose the agent and its web tools yourself.
• You want chat that reaches your whole workspace by default. Mem documents exactly that. Ask it to name the notes behind each claim, since the two Mem pages we read do not describe citations.
• You want the web in the answer. Tana's docs say its chat models search the internet for questions not related to your notes, and that they may include citation links. That helps with open questions and works against a closed set.

For the wider field, see the best second brain apps, what AI note-taking apps cost, and how Barside compares as an Obsidian alternative.

Details and limits in Barside

• Six passages per answer. At most two come from any one note or bookmark, so ask one thing at a time. A request such as “Summarize everything I wrote this year” needs far more than six passages.
• Word matching. A plural finds its singular, but a synonym does not. Words of one or two letters, such as “Q3” or “AI”, are not matched, so add a longer word from the note.
• One question, one answer. Ask library gives each question its own answer with sources instead of a running chat. A question can be up to 2,000 characters.
• The assistant is a different tool. The AI assistant (Ctrl+Shift+A) can search your library as one of its tools, and it can also search the web when your AI company offers web search. In Barside that covers Claude, ChatGPT and OpenRouter, while Gemini has no web search. For a notes-only answer, use Ask library.
• The research agent is the web tool. The research agent searches DuckDuckGo, reads up to 5 public pages and writes a note with numbered sources. The pages it read are saved as bookmarks with their text, so they can appear in later library answers unless you exclude them.
• Other AI apps. AI connections let Claude Desktop, ChatGPT or another MCP app search and read the workspaces you choose, read-only by default. You ask in that app, so check its own web search setting if you want a closed set.
• Systems. Ask library works the same on Windows 10 and 11, on Linux and in Barside for Mac.
• Cost. Barside is free, and your AI company bills you for what you use. In Settings → AI, under AI spending limit, turn on Limit what Barside's AI spends to set a daily, weekly or monthly cap.

Privacy: what leaves your computer

Your library stays in Barside's data folder on your computer, and the search runs there with nothing to download. When you press Ask library, your question and the matching excerpts go to the AI company you connected, and that company's data policy applies. Barside does not train any model on your notes.

Exclude a note that holds something sensitive, such as a pasted recovery code, before you start asking, because excluding it later cannot take back an excerpt that was already sent. The password vault, saved AI keys and the assistant's memory are never searched. Read more in how AI search uses your data and the AI you connect.

Works well with

Asking is one way into a library. These guides cover getting notes in, linking them, and the tools around Ask library.