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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description still adds genuinely new behavior: a registered key or Authorization Bearer header is required, and the example 'plan_me {}' shows the call works with no explicit params when credentials come from the header. That satisfies the bar for extra value beyond annotations.

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?

The 'WHEN:' label front-loads usage well and the invocation example is practical, but the opening 'Plans: me.' merely repeats the name and title, and the entitlement list is a dense comma-run that is harder to scan than a short bulleted enumeration would be.

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 compensates by listing exactly which fields an agent will receive, and it discloses the auth prerequisite. For a one-parameter read tool with strong annotations, that is nearly everything an agent needs; only the response shape (format, nesting, pagination-free?) is left implicit.

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?

There is a single parameter and the schema already documents it at 100% coverage ('Your ark_ key (or send Authorization: Bearer <key>). Registered keys only.'). The description only restates the registered-key requirement and demonstrates the empty-argument invocation, adding marginal meaning beyond the schema.

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 resource (your plan/entitlements) and enumerates concretely what it surfaces: active passes with days left, monthly credits, Office Desk, God Mode fires, priority arena access, fair-use count, renewal reminders, orders, and the weekly free credit drop. That enumeration makes the tool's scope unmistakable, though there is no verb and no direct differentiation from siblings like plan_list or plan_weekly_drop.

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 explicit 'WHEN:' block states the conditions that call for this tool (checking your own passes, entitlements, orders, weekly drop), and 'YOUR' signals self-scoped data. It stops short of naming when NOT to use it or pointing to plan_list / plan_checkout / plan_weekly_drop as alternatives.

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