Obsidian Canvas Boards
AgriciDaniel/claude-obsidian
Creates, inspects and updates Obsidian JSON Canvas boards in a vault, with text, file, link, group and edge nodes, using safe recoverable edits.
Answer a question from a second-brain vault by reading its own pages, citing the pages used, and saying plainly when the vault does not contain the answer.
Install Second Brain Query
$ npx skills add undefined-ui/second-brain-os --skill second-brain-query -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install undefined-ui/second-brain-os second-brain-query --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/undefined-ui/second-brain-os.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/second-brain-query .claude/skills/second-brain-query && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "second-brain-query" agent skill from https://github.com/undefined-ui/second-brain-os/tree/main/skills/second-brain-query into .claude/skills/second-brain-query/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "second-brain-query", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/undefined-ui/second-brain-os/tree/main/skills/second-brain-queryType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add undefined-ui/second-brain-os --skill second-brain-query -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install undefined-ui/second-brain-os second-brain-query --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/undefined-ui/second-brain-os.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/second-brain-query .agents/skills/second-brain-query && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "second-brain-query" agent skill from https://github.com/undefined-ui/second-brain-os/tree/main/skills/second-brain-query into .agents/skills/second-brain-query/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "second-brain-query", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add undefined-ui/second-brain-os --skill second-brain-query -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install undefined-ui/second-brain-os second-brain-query --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/undefined-ui/second-brain-os.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/second-brain-query .cursor/skills/second-brain-query && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "second-brain-query" agent skill from https://github.com/undefined-ui/second-brain-os/tree/main/skills/second-brain-query into .cursor/skills/second-brain-query/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "second-brain-query", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/undefined-ui/second-brain-os.git --path skills/second-brain-query--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add undefined-ui/second-brain-os --skill second-brain-query -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install undefined-ui/second-brain-os second-brain-query --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/undefined-ui/second-brain-os.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/second-brain-query .gemini/skills/second-brain-query && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "second-brain-query" agent skill from https://github.com/undefined-ui/second-brain-os/tree/main/skills/second-brain-query into .gemini/skills/second-brain-query/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "second-brain-query", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install undefined-ui/second-brain-os second-brain-queryInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add undefined-ui/second-brain-os --skill second-brain-query -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/undefined-ui/second-brain-os.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/second-brain-query .github/skills/second-brain-query && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "second-brain-query" agent skill from https://github.com/undefined-ui/second-brain-os/tree/main/skills/second-brain-query into .github/skills/second-brain-query/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "second-brain-query", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add undefined-ui/second-brain-os --skill second-brain-query -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install undefined-ui/second-brain-os second-brain-query --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/undefined-ui/second-brain-os.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/second-brain-query .opencode/skills/second-brain-query && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "second-brain-query" agent skill from https://github.com/undefined-ui/second-brain-os/tree/main/skills/second-brain-query into .opencode/skills/second-brain-query/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "second-brain-query", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
second-brain-query- GitHub stars
- 999
- Token cost
- ~550 tokens
- SKILL.md length
- 254 words
- Files
- 1
- Skills in repo
- 23
- Repo updated
- First seen
- Licence
- MIT
At a glance
Answer a question from a second-brain vault by reading its own pages, citing the pages used, and saying plainly when the vault does not contain the answer.
- Works in 5 steps: Start from index.md, not from a… → Follow links outward from the most… → Answer in plain language, with [[page]]… → …
- The user asks what they know about a topic
- SKILL.md covers Core rule, Workflow, Output format and Calibration
- Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
What it does
Second Brain Query is an agent skill from undefined-ui/second-brain-os. Answer a question from a second-brain vault by reading its own pages, citing the pages used, and saying plainly when the vault does not contain the answer. Use this skill whenever the user asks what they know about a topic, what they have read on something, what connects two ideas, what they have changed their mind about, or asks any question that should be answered from their own notes rather than general knowledge. Do NOT use for ingesting new material, for general questions the vault has nothing to do with, or…
Its SKILL.md is about 550 tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.
It sits in Knowledge Management, covering Second brain. The repository describes itself as: An AI second brain that maintains itself. Full guide, starter vault, agent skills and scripts for a self-organizing knowledge base in Claude Code and Obsidian. The licence is MIT.
When your agent uses it
- The user asks what they know about a topic
- What they have read on something
- What connects two ideas
- What they have changed their mind about
Example prompts
- “/second-brain-query”
Workflow steps
5 steps, taken from the first numbered list in SKILL.md.
- Start from index.md, not from a full-text sweep. The index is the map;
- Follow links outward from the most relevant pages, one hop at a time.
- Answer in plain language, with [[page]] references inline.
- Name the gaps. If the question has three parts and the vault covers two,
- Offer the next move when there is an obvious one: a source worth
What it can do on your machine
Read from SKILL.md and the folder at commit d6861cc. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md.
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Context cost
Second Brain Query loads about 550 tokens when it runs. Until then it costs about 149 tokens; SKILL.md has 254 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check passed
The automated check found no risky patterns in SKILL.md.
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.
SKILL.md
The full file from undefined-ui/second-brain-os at commit d6861cc, republished under its MIT licence (© undefined-ui). 254 words, ~550 tokens.
Download SKILL.mdSave it as
.claude/skills/second-brain-query/SKILL.md (or your agent's skills folder).- name
- second-brain-query
- description
- Answer a question from a second-brain vault by reading its own pages, citing the pages used, and saying plainly when the vault does not contain the answer. Use this skill whenever the user asks what they know about a topic, what they have read on something, what connects two ideas, what they have changed their mind about, or asks any question that should be answered from their own notes rather than general knowledge. Do NOT use for ingesting new material, for general questions the vault has nothing to do with, or when the user explicitly wants an answer from the open web.
Query the vault
A query that quietly falls back on general knowledge is the most damaging thing this system can do. The owner built the vault so answers would be grounded in what they actually read, and an answer that blends the model's priors with their notes is worse than no answer, because it cannot be checked.
Core rule
Every claim in the answer comes from a page in the vault and names that page. Anything you know but the vault does not is labelled as outside knowledge or left out.
Workflow
- Start from
index.md, not from a full-text sweep. The index is the map; reading it first keeps the context budget for actual pages. - Follow links outward from the most relevant pages, one hop at a time. Stop when new pages stop adding anything.
- Answer in plain language, with
[[page]]references inline. - Name the gaps. If the question has three parts and the vault covers two, say which one it does not.
- Offer the next move when there is an obvious one: a source worth ingesting, a synthesis page worth writing.
Output format
Plain prose, then:
Read: <pages consulted>
Not covered: <what the vault does not answer>Calibration
Reading too little is the common failure: answering from three pages when the vault has fifteen relevant ones. Reading everything is the opposite failure and burns the budget on pages that add nothing.
If the vault has nothing on the topic, say so in one sentence and stop. Do not pad the answer with general knowledge to avoid an empty result.
© undefined-ui, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
Just SKILL.md in skills/second-brain-query of undefined-ui/second-brain-os.
Open the folder on GitHubat commit d6861cc
Compare with similar skills
Second Brain Query next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Second Brain Query this skillundefined-ui/second-brain-os | 999 | — | ~550 | Automated safety check: Pass | MIT | |
| Obsidian Canvas BoardsAgriciDaniel/claude-obsidian | 15k | — | ~1.4k | Automated safety check: Pass | MIT | |
| 3D Brainnateherkai/AIS-OS | 1.6k | — | ~2.1k | Automated safety check: Pass | Custom licence | |
| Icm ArchitectRinDig/icm-architect | 1.8k | — | ~3.2k | Automated safety check: Pass | MIT | |
| Second BrainNicholasSpisak/second-brain | 735 | — | ~1.5k | Automated safety check: Notes | None | |
| Cascading Goal Trackerballred/obsidian-claude-pkm | 1.9k | — | ~1.5k | Automated safety check: Pass | MIT |
Similar skills
3D Brain
nateherkai/AIS-OS
A skill your agent uses when someone asks to build a 3D brain, visualize their AIOS or second brain, turn their knowledge into an interactive graph, or run /3d-brain or /3D brain.
Icm Architect
RinDig/icm-architect
Design any process, idea, problem, or body of knowledge into an ICM (Interpretable Context Methodology) workspace — folder structure as agent architecture — or restructure an existing folder, repo…
Second Brain
NicholasSpisak/second-brain
Set up a new Obsidian knowledge base with the LLM Wiki pattern.
Cascading Goal Tracker
ballred/obsidian-claude-pkm
Tracks three-year, yearly, monthly, and weekly goals in linked Markdown files, calculating completion percentages and flagging stalled goals.
Karpathy Wiki
SherwinQ/karpathy-wiki
A skill your agent uses when building or maintaining a personal knowledge base with LLM assistance.
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Audit an agent's context layout against the four places: system prompt, tools, history, tail.
Evals Bootstrap
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Scaffold a first eval suite for an agent: mine real failures into cases, write behavioural checks over traces, and generate the runner.
Gate Check
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Find the decisions in a pipeline that do not need the expensive model and propose the gate for each: a rule, a classic classifier, or a small model, with fail-closed routing.
Goal Test
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Turn a vague task into a testable definition of done and generate an executable goal-test script for it, optionally with a bounded retry loop around a headless agent.
Harness Audit
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Audit an agent's harness against the four rings: containment, guides, sensors, permissions.
Second Brain Chat Import
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Triage an exported chat history into what to ingest, what to archive and what to delete, with a privacy pass first.
Related
Categories
Questions about Second Brain Query
What does Second Brain Query do?
Answer a question from a second-brain vault by reading its own pages, citing the pages used, and saying plainly when the vault does not contain the answer. Second Brain Query is an agent skill from undefined-ui/second-brain-os. Answer a question from a second-brain vault by reading its own pages, citing the pages used, and saying plainly when the vault does not contain the answer.
When should I use Second Brain Query?
Second Brain Query fits situations like: the user asks what they know about a topic; what they have read on something; what connects two ideas; what they have changed their mind about.
How do I install Second Brain Query in Claude Code?
Run `npx skills add undefined-ui/second-brain-os --skill second-brain-query -a claude-code`. Or copy the skill folder (skills/second-brain-query in undefined-ui/second-brain-os) into .claude/skills/second-brain-query in your project. Claude Code loads it when a task matches its description.
How do I install Second Brain Query in Codex?
Run `npx skills add undefined-ui/second-brain-os --skill second-brain-query -a codex`. Or copy the skill folder (skills/second-brain-query in undefined-ui/second-brain-os) into .agents/skills/second-brain-query in your project. Codex loads it when a task matches its description.
Can I use Second Brain Query in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add undefined-ui/second-brain-os --skill second-brain-query -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/second-brain-query, .gemini/skills/second-brain-query, .github/skills/second-brain-query and .opencode/skills/second-brain-query in your project.
What does Second Brain Query need to run?
SKILL.md names no scripts, command-line tools or credentials: Second Brain Query is instructions for the agent only.
Does Second Brain Query access the network?
SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.
Is Second Brain Query safe to install?
Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.
What licence does Second Brain Query use?
Second Brain Query is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does Second Brain Query use?
About 550 tokens (SKILL.md is roughly 2.2k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.
What are the alternatives to Second Brain Query?
Skills that share tags, products or a category with Second Brain Query: Obsidian Canvas Boards (AgriciDaniel/claude-obsidian, 15k stars), 3D Brain (nateherkai/AIS-OS, 1.6k stars), Icm Architect (RinDig/icm-architect, 1.8k stars) and Second Brain (NicholasSpisak/second-brain, 735 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Second Brain Query?
undefined-ui (a GitHub user) maintains it in undefined-ui/second-brain-os, which has 999 GitHub stars. The repository holds 23 skills in this directory. The repository was last updated on September 29, 2026.
Source: undefined-ui/second-brain-os on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.