Your access + meter

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

Annotations already cover readOnly, idempotent and closed-world, so the safety profile is handled. The description adds genuinely new behavioral context by disclosing what the response contains (identity, entitlement, daily usage, access instructions) and that it acts as the explainer for refused/missing tools — valuable given there is no output schema.

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 tightly packed sentence with the highest-value content (identity/entitlement/usage) front-loaded before the diagnostic clause. No filler, though the telegraphic noun-phrase style slightly reduces readability.

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-parameter, annotation-covered tool with no output schema, the description compensates by enumerating the returned fields and the diagnostic role. Missing only an explicit statement of when to invoke it and whether authentication is required.

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, which is the baseline-4 case. There is nothing for the description to disambiguate beyond what the empty schema already conveys.

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 names the exact payload — identity, entitlement, daily usage, access instructions — which is a specific and distinguishable purpose for a meta/introspection tool sitting among market-data siblings. It lacks a verb (all noun phrases), but the resource is unambiguous and no sibling overlaps it.

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?

'Explains missing/refused subscriber tools' implies when this is useful — as a diagnostic after another tool is denied or absent — but it never states that explicitly, nor says whether to call it first, or that it is the only tool that works without subscriber entitlement. Usage is inferable, not stated.

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