Arc Status

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds substantive context beyond that: it discloses the guardrails the server was launched with (read-only mode, origin rules, audit log) and the idle/activity gate, which are behavioral facts an agent needs and cannot derive from annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

A single sentence, front-loaded with "Report Arc state" so the purpose lands immediately, followed by a dense but relevant enumeration of the reported fields. The list is long, but each item corresponds to a distinct thing an agent would need to know, so little is wasted.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

There is no output schema, so the description must carry the return-value burden, and it does so thoroughly by naming every reported field. For a zero-parameter, read-only status tool this leaves nothing material ambiguous.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool takes zero parameters, so per the rubric the baseline is 4. The description nonetheless explains what a call with no tab_id resolves to, which is a useful semantic note even without parameters.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (Report) and resource (Arc state) and enumerates the concrete dimensions returned: version, frontmost status, owned tabs, agent window details, idle time, activity gate, agent space, tab_id resolution, leftover tabs, and server guardrails. This clearly separates it from diagnostic siblings like cdp_status or snapshot.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

"Call it first" gives an explicit ordering directive, which is real usage guidance. It does not, however, name an alternative or state when not to call it, so it falls short of a full when/when-not pairing.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.