Install the Cortex plugin.

Local projects use the CLI

The plugin's skill installs the official CLI on first use when needed. It supports macOS and Linux on arm64 and x86_64, and verifies the release checksum. Linux requires glibc 2.36 or later.

The assistant uses CLI 0.5.0 or later and cortex login --email, then cortex login --code-stdin. It saves your name and verifies your Brain. The CLI reads each folder's preferred .cortex/config.toml. Existing sign-in and Brain selection are preserved.

The assistant installs a missing or older CLI with:

curl -fsSL https://www.thesecondbrain.company/cli/install.sh | bash

Download the CLI installer for the assistant to run bash install.sh, or use the same installer from the public CLI mirror. No Rust toolchain or checkout is needed.

CLI setup is ready when cortex --version, cortex account show, cortex config, and cortex whoami succeed for the intended Brain. The assistant runs each read-only readiness check in its own tool call and inspects the result before continuing. Guide downloads and installers run separately. It uses the verified absolute binary path when needed and handles PATH and runtime recovery internally without asking you to edit shell files, configure tools, or open a terminal.

Once the CLI verifies your account and Brain, the assistant disables Cortex's MCP server in that local client's settings and verifies the change. The plugin and its skills stay installed. Claude Code applies this setting to the current project; onboarding another project repeats the step. Clients without a working CLI keep the MCP connection for setup and knowledge access.

When ready, open a new chat in the same project and ask "What can I do with my Brain?" You can always ask your Brain what it can help with. No technical handoff, interview, or knowledge save is required to finish installation.

Use MCP when the CLI is unavailable

Hosted clients use the plugin's MCP connection. Use it locally too when there is no supported binary, or CLI installation or execution remains blocked after permitted recovery. Connect through your client's native OAuth flow to https://www.thesecondbrain.company/app/api/mcp/brain.

Choose the intended Brain during browser consent, then verify it with MCP whoami before accessing knowledge. Local project files cannot switch this connection; reconnect to choose another Brain. Installation is complete when the plugin's instructions and tools load in a fresh session. Knowledge setup also requires a verified Brain.

When changing transport, preserve any pending write's original Brain, input, and request ID. Check a known run ID with cortex runs get or MCP wait after verifying the Brain. Report uncertainty if no run ID or result can be recovered.

Download the complete package

Download the Cortex plugin archive and its SHA-256 checksum. Verify the checksum before extracting the archive.

Save both files in the same folder and run shasum -a 256 -c cortex.tar.gz.sha256 from that folder. The checksum names the archive by its filename.

If your assistant's shell says Could not resolve host while this page opens, its network sandbox may be blocking DNS. Have it retry the same URLs with authorized network access before treating the website as unavailable.

Install in Codex or ChatGPT desktop

1. Extract the verified archive into a temporary folder and compare its .codex-plugin/plugin.json version with the installed Cortex manifest and codex plugin list. Install when absent. Replace only ~/.agents/plugins/cortex when older. Keep a current or newer version, sign-in, and Brain selection.
2. Add a cortex entry to ~/.agents/plugins/marketplace.json, preserving other plugins. Use a personal marketplace named personal if the file is new. The local source path is ./.agents/plugins/cortex, resolved from your home directory.
3. Install with codex plugin add cortex@personal, using the marketplace file's actual name if it differs, or select Cortex from that marketplace in the desktop Plugins Directory. Restart the desktop app if the entry does not appear. Verify the installed version, then continue setup in this chat. A running chat can retain older instructions until the fresh chat after setup.

{
  "name": "personal",
  "interface": { "displayName": "Personal Plugins" },
  "plugins": [
    {
      "name": "cortex",
      "source": { "source": "local", "path": "./.agents/plugins/cortex" },
      "category": "Productivity",
      "policy": { "installation": "AVAILABLE", "authentication": "ON_USE" }
    }
  ]
}

If Cortex does not appear in the public Plugins Directory, use this package and personal marketplace. A website URL alone cannot register a plugin in that directory. ChatGPT workspace marketplace import accepts GitHub repositories, so this website address cannot be used as its source.

Install in Claude

Claude Code 2.1.224 or later can add the Cortex Claude marketplace and install its complete plugin. The marketplace verifies the ZIP archive against a pinned SHA-256 digest. For every install request, inspect claude plugin list --json and compare the installed version with the catalog's Cortex entry. The version belongs to that plugin entry, not the catalog root. A loaded skill does not establish that the plugin is current.

claude plugin marketplace add https://www.thesecondbrain.company/plugins/claude/marketplace.json
claude plugin install cortex@cortex-plugins
claude plugin list

If Cortex is older, refresh the official marketplace and update the plugin in its existing scope. Marketplace refresh alone does not update an installed plugin. Keep a current or newer version and preserve unrelated plugins and settings. Respect managed policy.

claude plugin marketplace update cortex-plugins
claude plugin update cortex@cortex-plugins --scope <existing-scope>
claude plugin list --json

Verify the installed version, then continue the published setup in this chat even if the running session retains older instructions. A fresh chat after setup loads the updated package in a new Claude Code session. The CLI's generic restart notice does not add a separate desktop-app restart step. Use local CLI email-code sign-in without starting MCP OAuth. A CLI-installed plugin may appear in Claude Desktop with a disabled Connect button; that control does not add an account-level connector.

For Claude chat or Cowork on a paid plan, download the Claude plugin ZIP and its SHA-256 checksum. Save both in one folder and run shasum -a 256 -c cortex-claude.zip.sha256.

In Claude, open Customize > Plugins > Add > Upload plugin and select the ZIP. Compare the installed version with the verified ZIP's plugin manifest and upload a newer complete ZIP when needed. Hosted manual uploads require the host's controls; an assistant without those controls must report the required step. Local Claude Code setup stays in chat. Connect hosted Cortex through native OAuth when local CLI execution is unavailable.

To connect Claude chat or Desktop without a plugin, open Customize > Connectors > Add custom connector. Name it Cortex and use https://www.thesecondbrain.company/app/api/mcp/brain as the remote MCP URL. The Cortex browser page sends the sign-in email and returns to Claude after consent. Use this path when a CLI-installed plugin shows a disabled Connect button. The custom connector supplies tools; upload the ZIP to add the knowledge skill in Claude chat.

Other AI clients

Clients that cannot install a local plugin can connect to the shared remote MCP endpoint at https://www.thesecondbrain.company/app/api/mcp/brain through their own connection flow. Sign up or sign in with your email during OAuth. Private knowledge requires current Brain membership and OAuth approval.

The complete agent guide is also available at /llms.txt for clients that can open plain-text resources.