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Agent skill

Second Brain Review

by undefined-ui in undefined-ui/second-brain-os

Produce a periodic review of a second-brain vault: what was added, which topics are growing, what contradicts what, which questions are still open, and what is worth reading next.

MITAuto-check passedKnowledge Management

Install Second Brain Review

skills CLI
$ npx skills add undefined-ui/second-brain-os --skill second-brain-review -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install undefined-ui/second-brain-os second-brain-review --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ 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-review .claude/skills/second-brain-review && rm -rf skills-src

Use ~/.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/

Facts

Skill name
second-brain-review
GitHub stars
1k
Token cost
~550 tokens
SKILL.md length
210 words
Files
1
Skills in repo
23
Repo updated
First seen
Licence
MIT

At a glance

Produce a periodic review of a second-brain vault: what was added, which topics are growing, what contradicts what, which questions are still open, and what is worth reading next.

  • Works in 6 steps: Diff the period. New and updated pages… → Find the clusters. Which concepts gained… → Surface contradictions recorded during… → …
  • The user asks for a weekly
  • 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 Review is an agent skill from undefined-ui/second-brain-os. Produce a periodic review of a second-brain vault: what was added, which topics are growing, what contradicts what, which questions are still open, and what is worth reading next. Use this skill whenever the user asks for a weekly or monthly review, asks what changed in their vault, what they have been learning about lately, or what they should look at next, and when a scheduled review task fires. Do NOT use for structural linting, for ingesting sources, or for answering a specific factual question.

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 and Linting and formatting. 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 for a weekly
  • Asks what changed in their vault
  • What they have been learning about lately
  • What they should look at next

Example prompts

  • “/second-brain-review”

Workflow steps

6 steps, taken from the first numbered list in SKILL.md.

  1. Diff the period. New and updated pages since the last review, from
  2. Find the clusters. Which concepts gained the most links. That is where
  3. Surface contradictions recorded during the period and still unresolved.
  4. List open questions from concept and synthesis pages.
  5. Find the neglected. Pages linked often but thin, or gaps in index.md
  6. Recommend three things to read or write next, each tied to a specific

What it can do on your machine

Read from SKILL.md and the folder at commit c7fa35b. 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 Review loads about 550 tokens when it runs. Until then it costs about 131 tokens; SKILL.md has 210 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~131
When it runs · the whole SKILL.md, loaded when a task matches
~550

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 c7fa35b, republished under its MIT licence (© undefined-ui). 210 words, ~550 tokens.

Download SKILL.mdSave it as .claude/skills/second-brain-review/SKILL.md (or your agent's skills folder).
name
second-brain-review
description
Produce a periodic review of a second-brain vault: what was added, which topics are growing, what contradicts what, which questions are still open, and what is worth reading next. Use this skill whenever the user asks for a weekly or monthly review, asks what changed in their vault, what they have been learning about lately, or what they should look at next, and when a scheduled review task fires. Do NOT use for structural linting, for ingesting sources, or for answering a specific factual question.

Review the vault

Capture systems fail at the point where nothing comes back out. A review is the loop that closes: it turns a week of ingestion into something the owner reads and acts on, and it is what makes the vault feel alive rather than archival.

Core rule

A review reports on the vault, not on the agent's activity. Nobody needs to know how many tool calls ran; they need to know what they now know.

Workflow

  1. Diff the period. New and updated pages since the last review, from log.md and frontmatter dates.
  2. Find the clusters. Which concepts gained the most links. That is where the owner's attention actually went, which is often not where they think it went.
  3. Surface contradictions recorded during the period and still unresolved.
  4. List open questions from concept and synthesis pages.
  5. Find the neglected. Pages linked often but thin, or gaps in index.md that keep getting referenced.
  6. Recommend three things to read or write next, each tied to a specific page.

Output format

## Week of <date>

Added: <n> pages, <n> sources ingested

### Where your attention went
<two or three sentences on the clusters>

### Unresolved
<contradictions and open questions, each linked>

### Thin spots
<pages that are referenced more than they deserve given their content>

### Next
1. <specific action tied to a page>
2.
3.

Calibration

Reviews that list everything get skimmed and then ignored. Keep it under a page. Three recommendations, not ten. If a week produced nothing worth reporting, say that in one line instead of manufacturing insight.

© 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-review of undefined-ui/second-brain-os.

Open the folder on GitHubat commit c7fa35b

Compare with similar skills

Second Brain Review 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.

Second Brain Review compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Second Brain Review this skillundefined-ui/second-brain-os1k—~550Automated safety check: PassMIT
Second Brain LintNicholasSpisak/second-brain736—~1kAutomated safety check: NotesNone
Second Brain DelintPieroSierra/SecondBrain152—~1kAutomated safety check: PassNone
Second Braincoreyhaines31/makerskills848—~2.9kAutomated safety check: PassMIT
Second Brain LintPieroSierra/SecondBrain152—~2.1kAutomated safety check: PassNone
Mindbasefrankchu91/mindbase-llm-wiki128—~1.1kAutomated safety check: PassMIT

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    NicholasSpisak/second-brain

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More from undefined-ui/second-brain-os

All 23 skills in this repo

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  • Context Audit

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    Audit an agent's context layout against the four places: system prompt, tools, history, tail.

    1k GitHub stars~802 tokensUpdated today
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  • Evals Bootstrap

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    1k GitHub stars~786 tokensUpdated today
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  • Gate Check

    undefined-ui/second-brain-os

    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.

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  • Harness Audit

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    Audit an agent's harness against the four rings: containment, guides, sensors, permissions.

    1k GitHub stars~855 tokensUpdated today
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  • Second Brain Chat Import

    undefined-ui/second-brain-os

    Triage an exported chat history into what to ingest, what to archive and what to delete, with a privacy pass first.

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Categories

Questions about Second Brain Review

What does Second Brain Review do?

Produce a periodic review of a second-brain vault: what was added, which topics are growing, what contradicts what, which questions are still open, and what is worth reading next. Second Brain Review is an agent skill from undefined-ui/second-brain-os. Produce a periodic review of a second-brain vault: what was added, which topics are growing, what contradicts what, which questions are still open, and what is worth reading next.

When should I use Second Brain Review?

Second Brain Review fits situations like: the user asks for a weekly; asks what changed in their vault; what they have been learning about lately; what they should look at next.

How do I install Second Brain Review in Claude Code?

Run `npx skills add undefined-ui/second-brain-os --skill second-brain-review -a claude-code`. Or copy the skill folder (skills/second-brain-review in undefined-ui/second-brain-os) into .claude/skills/second-brain-review in your project. Claude Code loads it when a task matches its description.

How do I install Second Brain Review in Codex?

Run `npx skills add undefined-ui/second-brain-os --skill second-brain-review -a codex`. Or copy the skill folder (skills/second-brain-review in undefined-ui/second-brain-os) into .agents/skills/second-brain-review in your project. Codex loads it when a task matches its description.

Can I use Second Brain Review 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-review -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-review, .gemini/skills/second-brain-review, .github/skills/second-brain-review and .opencode/skills/second-brain-review in your project.

What does Second Brain Review need to run?

SKILL.md names no scripts, command-line tools or credentials: Second Brain Review is instructions for the agent only.

Does Second Brain Review 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 Review 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 Review use?

Second Brain Review 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 Review 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 Review?

Skills that share tags, products or a category with Second Brain Review: Second Brain Lint (NicholasSpisak/second-brain, 736 stars), Second Brain Delint (PieroSierra/SecondBrain, 152 stars), Second Brain (coreyhaines31/makerskills, 848 stars) and Second Brain Lint (PieroSierra/SecondBrain, 152 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Second Brain Review?

undefined-ui (a GitHub user) maintains it in undefined-ui/second-brain-os, which has 1,009 GitHub stars. The repository holds 23 skills in this directory. The repository was last updated on October 7, 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.