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 adds genuinely new context by disclosing the returned content and noting it is 'Free' (no cost impact), which is useful behavioral information not in the 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?

A single front-loaded sentence that packs the resource, the returned fields, and the cost note with no waste. Everything earns its place.

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 parameters and no output schema, the description usefully enumerates what is returned, covering the main completeness gap. It stops short of clarifying the boundary with get_credit_balance, which would round it out fully.

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 there is nothing to document and the baseline is 4. The description doesn't need to compensate for any parameter gap.

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 ('show') and resource (monthly plan and credit balances) and even enumerates returned fields (plan, status, renewal time, cancel_at_period_end). It overlaps conceptually with the sibling get_credit_balance but doesn't explicitly differentiate itself from 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?

Usage is only implied ('show your monthly plan') with no explicit when-to-use or when-to-use-instead-of guidance. It does not point to siblings like get_credit_balance or list_subscription_plans, leaving the agent to infer which tool covers which slice.

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