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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds real value by disclosing the returned payload composition (subscriber, addresses, line items, discount codes, policies, payment method, billing dates), which matters because there is no output schema. It says nothing about not-found behavior, permissions, or id format, which is why this sits at 3 rather than higher.

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?

A single front-loaded sentence with no filler. Slightly list-heavy, but every enumerated item (line items, discount codes, billing dates) carries information about what the caller receives.

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 no output schema, the description usefully stands in for the return shape. However, it leaves out failure modes (invalid or missing subscription id) and any note on data freshness or scopes, which are meaningful gaps for a single-record fetch in a billing context.

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 schema description already explains that the id comes from recurpay_list_subscriptions. The tool description adds no parameter-level meaning beyond that, so the 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 and resource ('Get one subscription') and enumerates the composed sub-resources returned, which distinguishes it from the list variant by name ('one'). It does not explicitly contrast with recurpay_list_subscriptions or recurpay_get_subscriber, but the singular/plural distinction is legible from the sibling names.

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 implied: fetch a single subscription when you have an id. No explicit when-to-use or when-not-to-use statement, and no pointer to alternatives such as recurpay_list_subscriptions (to find ids) or recurpay_get_subscriber (for subscriber-centric reads).

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