Claude usage limits

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

Annotations already declare readOnlyHint/idempotentHint/openWorldHint, so the safety profile is covered. The description goes further with genuinely non-obvious traits: the data source is an UNOFFICIAL, undocumented endpoint, and 'null fields plus `warning` mean partial data'. It doesn't state rate limits or caching beyond the no-polling warning, but this is well above the annotation baseline.

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 sentences, each carrying distinct load: what is returned, how to interpret partial data, and how often to call. The critical 'what/when' content is front-loaded and there is no filler.

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?

No output schema exists, so the description must carry the return-shape burden, and it does — naming the window types, the percent fields, the reset time, and the `windows` list. Combined with the partial-data warning, an agent has everything needed to call and interpret this tool.

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 no parameters, so the 4 baseline applies. The description's field-level detail (session_*, weekly_*, windows) actually documents return shape rather than inputs, which is useful but doesn't change the zero-parameter picture.

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 ('Return the Claude subscription's usage limits') and enumerates exactly which figures come back (5-hour session window, weekly window across all models, used/remaining percent, reset time). There are no siblings to disambiguate from, but the scope is unambiguous on its own.

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?

Gives explicit timing guidance — 'Call it once before expensive work; do not poll in a loop' — which tells the agent both when to invoke it and a concrete anti-pattern to avoid. That is the strongest form of usage guidance available for a zero-param read tool.

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