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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, and the description reinforces this with 'No arguments, card access or writes' — the card-access note adds auth-scope context beyond the hints. The 'null aiMonthlyMessages means uncapped, not zero' line is a genuinely useful semantic disclosure about a null sentinel that the output schema alone may not convey.

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?

Three short sentences, each earning its place: what it reads, when to call it, and the null-sentinel caveat. Front-loaded with the resource before the routing hint.

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 an output schema present, return structure need not be restated, and the description covers the one remaining ambiguity (null meaning uncapped). Nothing an agent needs to call it correctly is missing.

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?

Zero parameters, so the baseline is 4; the description correctly confirms 'No arguments,' matching the empty schema with additionalProperties=false. Nothing more is required.

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 (Reads) plus the exact resource set: the authenticated account's plan, monthly AI limits and current usage. No sibling tool (review cards, SQL, workspaces) overlaps with this scope, so an agent can route to it unambiguously.

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?

Names the triggering intent explicitly: 'for plan or remaining-allowance questions.' That is a clear use context, but it offers no exclusions or named alternatives for adjacent questions (e.g., per-workspace usage).

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