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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds critical behavioral context the annotations cannot carry: the output is ready-made user-facing copy with Markdown links that must be relayed verbatim, with explicit prohibitions on summarizing, reordering, or dropping links. That is exactly the kind of non-obvious trait an agent needs.

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 a dense single block, but it is front-loaded with the core purpose and every clause earns its place (trigger conditions, intent semantics, relay instructions). Slightly long, though nothing is redundant with structured fields.

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?

There is no output schema, so the description carries the burden of describing the return value — and it does ('ready-made, user-facing copy whose Markdown links point at the exact purchase pages'), plus how to present it. For a zero-required-param read tool this is fully sufficient.

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?

Schema coverage is 100% and the enum values are already documented, so the baseline is 3. The description adds value by explaining the consequence of each intent — topup/upgrade change how the response is 'ordered for that purchase path' — which the schema only hints at.

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 states a specific verb+resource ('Show the user their current credit balance and plan') and immediately scopes it beyond a bare balance call by adding 'live plan/credit-pack pricing and direct purchase links'. This lets an agent distinguish it from siblings like popcraft_balance or popcraft_transactions without opening their schemas.

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?

It gives explicit triggers: 'use this as the recovery step after a `popcraft_generate_*` call fails with insufficient credits, or whenever the user asks about pricing/plans/credits.' It further routes between parameter choices (topup for out-of-credits, upgrade for model-locked). Nothing is left to inference.

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