Fetch a vault handle for a host from the browser-cookies AgentDB namespace. Raw cookie values are NEVER returned — only the opaque handle plus expiry / AIDefence verdict. Use when native WebFetch is wrong because you need real browser automation — JS-heavy SPA scraping, login flows with cookie re...
AI agents call browser_cookie_use to retrieve information from Claude Flow without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Despite the sensitive nature of cookies, this tool's documented behavior is to READ and return metadata (handles and verdicts) rather than expose raw values or perform actions. The intent is to support browser automation workflows, but the tool itself performs data retrieval with security gates (PII filtering, opaque handles).
From the tool's definition Tool description states 'Fetch a vault handle' and 'Raw cookie values are NEVER returned — only the opaque handle'. The primary action is retrieval of metadata (handle, expiry, AIDefence verdict) about stored cookies, not modification or execution.
Attacks that exploit this kind of access
Fetch a vault handle for a host from the browser-cookies AgentDB namespace. Raw cookie values are NEVER returned — only the opaque handle plus expiry / AIDefence verdict. Use when native WebFetch is wrong because you need real browser automation — JS-heavy SPA scraping, login flows with cookie reuse, replay against DOM-drifted versions, AIDefence PII gating before content reaches Claude. For static HTML pages, native WebFetch is faster and free. It is categorised as a Read tool in the Claude Flow MCP Server, which means it retrieves data without modifying state.
Register the Claude Flow MCP server in PolicyLayer and add a rule for browser_cookie_use: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Claude Flow. Nothing to install.
browser_cookie_use is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the browser_cookie_use rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for browser_cookie_use. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
browser_cookie_use is provided by the Claude Flow MCP server (claude-flow). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.