CoAgent8 - MCP bridge to coding CLIs

Second opinions and Git reviews from another coding agent, inside your chat.

By Oktawian Wybieralski

CoAgent8 connects VS Code chat to OpenAI Codex, Claude Code and Google Antigravity (agy). Ask another agent to examine a design, investigate a bug or review your Git changes, then continue the discussion in the same session. Your chat stays in VS Code; the other agent runs on your own installed and signed-in CLI, in a read-only profile.

The extension bundles the CoAgent8 MCP server, so nothing else needs to be installed except the CLIs themselves. It can also add CoAgent8 to the CLIs' own chats.

Preview. Versions below 1.0.0 are previews for testers. CoAgent8 reads and advises; it does not yet let the other agent write changes. See known limitations.

Requirements

Model access and billing follow your CLI account. For SSH or WSL, install the extension on the remote host, where Node.js and the CLIs must be available too. There the server works in chat, but the CoAgent8 commands are not available: run npx -y coagent8@next status (or setup, cleanup) in that machine's terminal and edit ~/.coagent8/config.json there.

Quick start

1. Install the extension. The first start shows one notice with the CLIs it found, or an offer to set one up.
2. Run CoAgent8: Manage Coding CLIs to install a CLI or sign in, if needed.
3. In MCP: List Servers, start CoAgent8 and accept VS Code's trust prompt; enable its tools in the chat's tool picker.
4. Ask: "Use CoAgent8 doctor with scope health to check the coding agents available for this workspace." Fix anything it reports as missing or signed out.
5. Ask for a consultation or a review, as below.

VS Code starts and stops the bundled server itself. A manual CoAgent8 entry in your MCP configuration takes precedence over the extension's.

Example requests

Ask in ordinary language; your chat agent fills in the tool arguments. Name a backend when you want a specific agent.

Use CoAgent8 consult with Codex to assess this retry strategy. Focus on concurrent writers and explain the failure cases.

Use CoAgent8 review with Claude to review my uncommitted changes. Check error handling and compatibility, and cite the affected files.

Ask Antigravity through CoAgent8 (backend agy) for a second opinion on this module design.

Continue the previous CoAgent8 session and ask how the proposed fix handles cancellation.

Ask CoAgent8, with a model below 1 USD per million output tokens, whether this regular expression is safe.

A review's verdict is derived by CoAgent8 from the other agent's findings: an incomplete review, a serious finding or a failed check makes it BLOCKED. It is still one agent's judgement, not a test run.

Tools

Answers come back as Markdown with the backend, model, duration and session handle; passing the handle continues the same conversation. Your chat host controls tool visibility, progress and approvals.

Commands

Press F1 (or Ctrl+Shift+P, Cmd+Shift+P on macOS), type CoAgent8 and choose a command:

Manage Coding CLIs

The list shows Codex CLI, Claude Code CLI and Antigravity CLI, installed or not, with their state (ready and version, sign-in needed, not installed), whether CoAgent8 is in the CLI's own chat, and the installation in use. "Its own chat" means the chats of Codex, Claude Code and Antigravity themselves, in their VS Code extensions and terminals; VS Code chat uses CoAgent8 either way. When there is something to do, the list ends with Add CoAgent8 to All CLI Chats or Update CoAgent8 in All CLI Chats.

A CLI's menu shows only what applies, and reopens with fresh checks after each action:

• Installations: every installation found, the one in use marked; choose another to use it.
• Install: Install VS Code Extension (recommended) or Install Standalone CLI (the vendor's official installer), each while that kind is missing; Choose Executable selects a CLI from any folder after checking it.
• Chat: Sign In, Add CoAgent8 to Its Chat or Update CoAgent8 in Its Chat. A chat entry you wrote yourself is never changed.
• Skills: Manage Skills for this CLI.
• Remove: Remove CoAgent8 from Its Chat, and Uninstall VS Code Extension or Uninstall Standalone CLI for what CoAgent8 installed.

Installations are found without starting them: the vendor extension's copy, every folder on PATH, the official installers' folders and the configured file. A selection is stored as backends.<id>.executable in config.json, so VS Code chat, the CLI chats and the coagent8 command all use it. CoAgent8 never downloads or stores CLI binaries; every CLI stays in its vendor's location.

Installer, sign-in and removal commands are typed into a terminal without running them: press Enter there, then choose Check Now (or Reload Window if an installer changed PATH). Sign-in is read from each CLI's own silent check; it never starts a login or a model turn.

Uninstall VS Code Extension opens the extension's page, where VS Code's own Uninstall and Restart Extensions remove it from every running extension without reloading the window. CoAgent8 finishes once the extension is gone, including the agy binary the Google Antigravity extension downloads to ~/.gemini/bin. Uninstall Standalone CLI types the vendor's removal commands into a terminal; sign-ins and histories (~/.codex, ~/.claude, ~/.gemini) stay.

After a change to a CLI's chat, one notice offers Restart Extensions: the vendor chat extensions load MCP servers only when they start. The window and chat histories stay, but replies in progress stop. New terminal sessions see the change without a restart.

Manage Model Approvals

The first step shows the price rules (ask above a price, ask above a multiple of the backend's default) and each backend with its model counts; the second lists the backend's models, most expensive first, with their price and what decides them; the third sets one model's rule: Allow, Ask Every Time, Deny or Price Rules. A rule for a model covers its effort variants. Rules are saved in config.json, so they apply in every client, including the ones that cannot show CoAgent8's approval form.

Manage Skills

Choose a CLI, an action that has packages to change, then the packages (all selected); Back returns one step. Disabled skills move to ~/.coagent8/disabled-skills/<client>/ and come back when enabled. Your choices are kept in config.json, so a repair or update does not undo them, and a skill you edited is never overwritten. Start a new chat to see changes.

Settings

Run CoAgent8: Open Settings or search for CoAgent8 in Settings. Every setting is machine-scoped: a workspace cannot change backends or models.

A setting you save, even with its default value, takes precedence over the same option in config.json; a setting you never set keeps the file's value, and an empty model setting keeps the file's model. The CLIs and other MCP hosts read only the file. Changing a setting restarts the server on its next use. If Node.js is not on PATH, set its absolute path, for example "coagent8.nodePath": "C:\\Program Files\\nodejs\\node.exe".

Data and privacy

• The other agent's CLI sends your prompt and workspace context to its provider; CoAgent8 is not offline inference.
• Answers are redacted for recognized credential formats, and diagnostics also for home paths and sensitive settings. Redaction cannot guarantee that private source content is removed.
• Sessions and their history stay in the extension's storage (globalStorage/okidev.coagent8-mcp). A session handle expires after two hours without use. The history archive is best effort, up to 10 MiB per session and 100 MiB in total, and old archives are removed after seven days; coagent8_HISTORY=off turns it off.
• A model with an unknown or approximate price, or priced at or above your thresholds (by default 20 USD per million output tokens or twice the backend's default), runs only after you approve it in a form. Prices come from OpenRouter's public list and guide the approval; they are not your bill.

Uninstalling

Use the Extensions view. On VS Code's next full start, CoAgent8 removes what it added and you did not change: its entries in the CLIs' chats, its skills, its runtime copies and private backups. Another VS Code installation, such as Insiders, keeps its own entry. VS Code deletes the extension's storage with its sessions and history.

Kept: ~/.coagent8/config.json, your coagent8.* settings, CLI sign-ins and histories, entries you wrote or edited, and the CLIs or vendor extensions CoAgent8 installed: Manage Coding CLIs offers their removal again after a reinstall. To remove CoAgent8 from a CLI's chat without uninstalling, use Remove CoAgent8 from Its Chat.

Troubleshooting

For a reproducible problem, ask your chat agent to use doctor and issue, then check the generated report for private data before submitting it.

Known limitations

• Antigravity's own tools. agy gives the other agent your agy MCP servers and plugins, which CoAgent8 cannot turn off; doctor lists them and calls back into CoAgent8 are refused.
• Leftover agy processes on Windows. Cancelling an agy turn stops agy, but a process it started outside itself, such as one of its MCP servers, can keep running until it exits or the server stops.
• Approval forms. Not every chat shows MCP forms; Codex and the Antigravity chat did not when measured. Allow such models in Manage Model Approvals.
• Host deadlines. A chat host can stop a tool call before CoAgent8's own deadline.
• Restart Extensions restarts every extension: VS Code has no way to restart only the vendor chat extensions.
• On a remote extension host (SSH, WSL) the CoAgent8 commands are not available; use the coagent8 command in that machine's terminal. Virtual and untrusted workspaces are not supported.
• Icons, tool grouping and refreshing existing chats depend on the chat host.

Updates, support and license

The extension and its bundled server carry the same version as the npm package coagent8. Versions below 1.0.0 are VS Code pre-releases; every release has a new number, so VS Code offers Restart Extensions after an update. The Changelog tab shows the release history of user-facing changes.

Website | Issues and questions | Source | Documentation

Licensed under GPL-3.0-only. The extension includes LICENSE and the notices of its bundled dependencies in dist/THIRD_PARTY_NOTICES.txt.