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

Annotations already declare readOnlyHint=true, so the read-only safety profile is covered. The description adds the underlying REST endpoint (GET /subscriptions/{id}), which is mildly useful context, but discloses nothing about what is returned, error behavior, or the effect of expand on payload size.

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?

Three short clauses, front-loaded with the action and resource. The trailing REST endpoint is useful for backend-oriented agents, though 'Supports expand' is terse and could say more about what expansion does.

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 carries the burden of explaining the return value, and it does not — an agent cannot tell what a subscription object contains or how expand changes the response. For a simple two-parameter read tool with readOnlyHint this is adequate but has a clear gap.

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 both id and expand are already documented in the schema, including the comma-separated expand format. The description merely echoes 'by id' and 'supports expand' without adding syntax or constraint detail, 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 ('Fetch a single subscription by id'), and the word 'single' implicitly contrasts with the sibling swell_list_subscriptions. It does not name that sibling explicitly, so the differentiation is inferable rather than stated.

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 phrase 'by id' implies the precondition that a subscription id is required, but the description gives no when-to-use framing, no indication of when to prefer this over swell_list_subscriptions, and no guidance on the failure case of an unknown id.

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