update-subscription

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

Annotations already indicate destructiveHint=true and readOnlyHint=false, so the description does not need to repeat these. The description adds that renewal extends expiration and warns about max limits, which is consistent with the destructive flag. It also reiterates the need to renew before expiry. No contradictions; the description complements annotations with practical timing context.

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?

The description is moderately sized, with the main purpose in the first sentence. The second paragraph is a helpful tip that front-loads the essential information (body format and timing). The first paragraph includes somewhat generic context about permissions and expiry, which is useful but could be trimmed. Overall, well-structured and not verbose.

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 tool with a complex schema and no output schema, the description supplies enough context to call it correctly: it tells the agent to pass the new expirationDateTime before expiry, and to check limits. It does not cover the generic flags like confirm or includeHeaders, but these are likely consistent across tools and not essential for this purpose. The description is complete for the core operation.

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?

With 80% schema coverage, the description still adds significant value by explicitly stating the essential body parameter: 'Body: { expirationDateTime (ISO 8601, new expiry) }.' This clarifies that in the update operation, only the expiry field is required in the body, which is not immediately apparent from the schema that lists many optional properties. Additionally, the description highlights the subscriptionId parameter implicitly by its focus on renewal, and the schema itself clarifies the naming. This goes beyond the schema's existing documentation.

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 clearly states the tool's purpose: 'Renew a subscription by extending its expiry time.' It specifies the verb (renew), the resource (subscription), and the action (extending expiry). This distinguishes it from sibling tools like create-subscription, delete-subscription, and reauthorize-subscription, which have different actions.

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 description provides clear context on when to use this tool: 'Call before the current expirationDateTime to avoid missing notifications.' It also advises checking maximum extension limits for each resource type. However, it does not explicitly mention exclusions or when not to use it, but the sibling set makes that obvious. This is more than implied; it gives actionable timing guidance.

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