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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered; the closing 'Read-only: it changes no subscription' reinforces it with domain-specific specificity. The description goes further by explaining what the returned fields mean (current_plan and per-stack current flags indicate ownership; current_tier is a legacy class, not a plan), which is genuinely useful behavioral context beyond 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?

It is front-loaded with the core purpose, then moves to field interpretation and a safety note; every sentence is relevant. The 'Read-only: it changes no subscription' line is partially redundant with readOnlyHint, which keeps it from being maximally tight.

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, the description need not document return shapes, yet it still clarifies the three ambiguous output concepts (current_plan, per-stack current flag, current_tier), which is exactly the gap an agent would hit. Nothing needed to invoke a zero-parameter read tool 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?

The tool takes no parameters, so there is nothing for the description to disambiguate and the baseline of 4 applies. The description instead spends its words on output semantics, which is the right allocation for a zero-argument tool.

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 opens with a specific verb and resource ('Returns the plan the user holds') and enumerates the exact catalog covered (Handler Free, per-agent plans, Bundle, Chief, Pixel Pro add-on, monthly/annual price). That content is unmistakably different from siblings like get_usage or capabilities, so an agent can pick it without opening the schema.

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: an agent can infer this is the tool for pricing/plan-enumeration questions, and the note that 'current_tier is the legacy capability class, not a plan' steers away from a likely confusion with capabilities. There is no explicit statement of when to use this versus get_usage or when not to call it.

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