subscriptions_get_by_username

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds no behavioral context beyond that: no case-sensitivity note, no error or not-found behavior, no indication of what subscription data is returned.

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 a single front-loaded clause with no redundant wording, so it is efficient. It is arguably too terse to convey much beyond the name, but that is a completeness concern rather than a structural one.

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?

Given the low complexity (one required parameter) and existing read-only annotations, the description is minimally adequate. However, with no output schema and no note on what the returned subscription contains or how this lookup differs from sibling subscription-get tools, an agent must infer too much.

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 description coverage is 100%, so the single 'username' parameter is already documented in the schema. The description merely restates the lookup key and adds no syntax, format, or constraint details beyond what the schema provides, making the baseline 3 appropriate.

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 states a specific verb and resource ('Get subscription') and the lookup key ('by username'), making the purpose unambiguous. It implicitly distinguishes itself from siblings like subscriptions_get_by_user_id and subscriptions_get_by_short_uuid through the key, but never names or contrasts with those alternatives explicitly.

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?

There is no guidance on when to use this tool versus sibling lookups such as subscriptions_get_by_user_id, subscriptions_get_by_short_uuid, or subscription_info. No prerequisites, exclusions, or context for selection are provided.

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