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

Annotations already establish read-only, non-destructive, open-world behavior, so the description only needs to add semantics — and it does, by disclosing that attempts made before a migration from another subscription app are included, which is non-obvious counting behavior. No return shape or failure behavior is described.

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?

One front-loaded sentence carrying the definition and its key edge case, followed by the endpoint path. Nothing is redundant or buried.

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 single-param, read-only count with fully documented schema and annotations covering safety, the description is nearly sufficient. The main residual gap is that with no output schema it never confirms the return shape (a bare integer vs. an object), though the tool name implies a count.

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 subscription_id is fully documented (Shopify contract id, gid accepted), so the description adds no parameter meaning beyond the schema. Baseline 3 applies.

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 (count) and resource (successful billing attempts of a subscription), plus a scope qualifier that pre-migration attempts are included. An agent can distinguish it from the sibling list_billing_attempts, which enumerates rather than counts.

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: a count is what you want when you don't need the individual records, versus list_billing_attempts. The description never states when to prefer this tool over that sibling or any prerequisite, leaving the routing to inference.

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