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

Beyond readOnlyHint it discloses the visibility rule that determines the result set (who you can see) and the exclusion of ended subscriptions, plus the semantics of date_end when suspended. 'Read-only' restates the annotation, and pagination/ordering behavior behind `limit` is not described, so it falls just short of full transparency.

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?

Front-loaded with purpose, scope and exclusion before the per-parameter notes, and each sentence carries information. It runs long for a two-parameter list tool, and the status enum recitation is verbose given an output schema exists.

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 read-only list tool with annotations covering safety and an output schema covering return shape, the description supplies everything else an agent needs: whose subscriptions appear, what is filtered out, where to go instead, and how to use both parameters.

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 0%, so the description carries the load and largely does: `athlete` is explained as a usr_… handle sourced from list_athletes, with the omit-to-list-all default spelled out. `limit` is only glossed as 'max rows' with no default value, maximum, or paging cursor mentioned.

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?

Opens with a precise verb+resource and immediately parenthesizes the domain meaning ('a coach billing an athlete monthly via Stripe'), which no sibling tool covers. It is clearly distinguishable from list_athletes, list_my_invoices and the generic nolio_api_read.

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?

Explicitly defines the returned scope (subscriptions you bill as a coach, plus your own when billed as an athlete) and states the exclusion — ended subscriptions are not listed. It then names the alternative route for that excluded case ('read billing/payments/ with nolio_api_read'), which is exactly the when-not/alternative guidance an agent needs.

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