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

readOnlyHint=true already tells the agent this is a safe, non-mutating read. The description adds useful context by enumerating what the payload contains (free vs plan scans vs credits), but says nothing about auth requirements, staleness of the quota data, or rate limits.

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 short sentences with the return content front-loaded and the usage cue second. Every clause earns its place; the only minor issue is the slightly breathless dash-bounded enumeration.

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?

With no output schema, the description carries the return-value burden and does so adequately by naming the four quota components. For a zero-parameter read tool this is close to complete, though it stops short of describing units or what a zero/exhausted quota looks like.

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 correctly implies no inputs are needed — it is a pure account-state read.

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?

The description states the resource (the user's scan quota and plan) and enumerates the returned quantities — free scans, plan scans, credits, plan. It is a clear account/quota lookup distinguishable from siblings like scan_url or list_recent_scans, though the verb is implicit ("How many...") rather than a stated action.

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?

"Check this before starting several scans" gives a concrete trigger condition, which is more than most zero-param tools offer. However, it names no alternatives and gives no threshold for what counts as "several," leaving the when-to-use decision partly implied.

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