Computer use and browser use

Computer use gives Claude a screen, a cursor and a keyboard. Browser use gives it a browser specifically — pages, navigation, the accessibility tree, console and network entries.

They are the most capable and the most consequential tools in the stack.

Current toolsets

Toolset	Identifier	Definition overhead
Computer use	computer_toolset_20260801	~4,500 input tokens (~4,520 on Fable 5, Mythos 5, Opus 5 and Opus 4.8; ~4,590 on Sonnet 5)
Browser use	browser_toolset_20260801	~6,600 input tokens; all four optional members add ~880 more

Disabling zoom via configs removes about 410 tokens from the computer toolset. Earlier versions (computer_20251124, computer_20250124) have different, smaller overheads.

Screenshots come back as image input and are billed as such. A long computer-use session is mostly paying for pictures of screens.

What it does not do

• It does not run in a sandbox by default. On the CLI it drives your computer. Choose a sandbox environment deliberately.
• It is not immune to prompt injection. This is the central risk: a web page or a document can contain text addressed to the agent rather than to you. An agent that can click is an agent that can be talked into clicking.
• It is not cheap to leave declared. ~7,000 tokens per request for browser use, whether or not it gets called.

Using it responsibly

• Run it against a dedicated profile or account, never your primary authenticated session.
• Constrain it with permissions rather than trusting task scope.
• Assume any content it reads is untrusted input.
• Read the usage policy before deploying it against third-party services.