# SecondAgent · Agent Mode

> SecondAgent, the SecondStack agent mode, runs Claude Code in per-thread Docker sandboxes with 18+ built-in Skills — files, browser, diagrams, office docs, and persistent memory.

Canonical: <https://docs.secondstack.ai/features/ai-agent/>
Updated: 2026-07-07

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**SecondAgent** is SecondStack's agentic mode — it appears as the Cowork Agent inside the chat UI. It turns a chat into a working session with an AI coworker: it runs the **Claude Code** CLI inside an isolated, per-thread Docker sandbox, equipped with Skills for real tasks — reading and writing files, automating a browser, authoring diagrams and office documents, generating images, and remembering context across a session.

<p class="ss-mock-caption">The agent works in its own sandboxed workspace — here creating and running a file, then returning it.</p>

## How it runs

- Each agent session runs the **Claude Code CLI inside its own Docker sandbox container**, tied to a single chat thread, with an isolated workspace.
- Sandboxes run as a **non-root** user with baked, read-only tooling, keeping the runtime constrained.
- Files move in and out of the sandbox through presigned object storage, and generated artifacts are returned to the chat.

## Where it runs

SecondAgent supports two runtimes, which administrators can enable independently:

- **Cloud / server runtime** — sandboxes run on the platform's own infrastructure.
- **Local desktop runtime** — a companion desktop app (macOS, Windows, Linux) pairs to the platform and runs sandboxes on the user's own machine and folders.

## Skills

Skills give the agent concrete capabilities. SecondStack ships **18+ built-in Skills**, and the set is extensible with your own. They include:

- **File operations** — read, write, and manipulate files in the workspace.
- **Browser automation** — drive a real browser for research and web tasks.
- **Image generation** — create and edit images.
- **Diagram authoring** — produce diagrams (for example, draw.io).
- **Office documents** — author Word, Excel, PowerPoint, and PDF files.
- **Persistent memory** — carry context forward within a session.

Additional Skills can be added per user or overlaid for the whole organization.

## Billing

The agent can run against a **Claude subscription** (via OAuth) or against **API billing** through the gateway, depending on the profile an administrator configures.

## Related

- [SecondChat](/features/chat-app/) — where agent sessions start.
- [Knowledge Collections](/features/knowledge-collections/) — give the agent grounded context.
- [Cost Management](/features/cost-management/) — budget agent usage per key.