How much disk the HTTP cache uses

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

readOnlyHint=true already tells the agent this is a safe read, so the description doesn't need to restate that. It adds real value beyond the annotation by naming the API used and explicitly bounding what is measured (network cache only, not IndexedDB/Service Worker), which prevents misinterpreting the returned number.

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?

Two tight sentences: the action and scope come first, the caveat second. Nothing is repeated from the title or annotations and every clause carries useful information.

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?

For a zero-param read-only tool with no output schema, the description is essentially complete: it tells the agent what is measured and what is excluded. It stops short of saying what the return value looks like (number, units), which is a minor gap given there is no output schema to cover it.

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 input schema is empty and has no parameters, so there is nothing for the description to disambiguate. Baseline 4 applies for a zero-parameter tool.

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 and resource — report the size of the on-disk HTTP cache — and cites the underlying API (Services.cache2.asyncGetDiskConsumption). It explicitly distinguishes this measurement from IndexedDB, Service Worker caches and storage, which an agent could reasonably confuse it with.

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?

The scope note makes clear when this tool is the right one: for network-cache disk consumption rather than broader storage. It doesn't explicitly point to siblings such as browser_clear_cache or browser_memory_usage, but the exclusion language covers the main ambiguity.

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