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

Annotations already indicate read-only, non-destructive behavior, and the description adds context by specifying that only active subscriptions are returned and which fields appear (amounts, frequency, next billing date). This goes beyond the raw schema without contradicting any annotation.

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 sentence, front-loaded with the action and resource, and no filler. It covers the essential scoping and output fields efficiently.

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 simple parameterless read-only tool, the description is sufficient: it states what is listed, the filter (active), and the key output fields. It does not describe formatting or edge cases, but no output schema exists and the tool is low-complexity.

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?

There are zero parameters, so there is nothing the description needs to explain beyond the schema. The description focuses on the output rather than input, which is appropriate for a parameterless listing tool.

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 uses a specific verb ('List'), identifies the resource ('subscriptions'), and narrows scope to 'active' subscriptions while naming the returned fields. This clearly differentiates it from the create_subscription sibling and other list_* tools.

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 clearly establishes the tool's purpose for retrieving active subscription data, but it does not explicitly state when to use it over alternatives or mention any exclusions. The context is clear enough for an agent to know this is the read-only listing counterpart to create_subscription, though not fully explicit.

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