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

The description adds real behavioral context the annotations do not: the required credential (JWT or rk_ key) and the shape of the returned data (period_end for passes, runs_left for run packs). It does not, however, resolve the tension with readOnlyHint=false, which is surprising for a tool whose name and description clearly indicate a read/query of existing purchases.

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?

Two short sentences with no filler, and the auth requirement is front-loaded so the agent learns the blocker before anything else. Slightly suboptimal ordering in that the purpose of the call comes after the credential requirement.

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?

For a zero-argument read tool with no output schema, the description gives partial return-value hints (period_end, runs_left) but no pagination, ordering, or overall response shape. It is adequate but leaves the agent guessing what the payload looks like.

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 for the description to disambiguate beyond what the empty schema shows; the baseline of 4 applies. The parenthetical hints (period_end, runs_left) describe return fields rather than inputs, which is a small bonus.

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 enumerates the resource contents ('paid unlocks, passes (period_end) and run packs (runs_left)') and the title 'What you have bought' frames it, so an agent can infer this returns the caller's purchases. However, there is no explicit verb ('list'/'get') and no differentiation from plausible siblings like payouts_ledger, creator_earnings, or product_get.

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 only guidance is an auth precondition ('Requires a JWT or an rk_ key'), which is useful but is a prerequisite, not a when-to-use statement. Nothing says when to call this instead of payouts_ledger or creator_earnings, and no exclusions or alternatives are given.

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