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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful context beyond that: the record contains personal data with IP address and coordinates removed, and it names the underlying endpoint. It does not mention pagination or auth, but those are minor for a single-record fetch.

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?

Two tight fragments with the key scope front-loaded and zero filler. The trailing 'GET /subscribers/{id}' is slightly redundant with the tool name but useful for API mapping, keeping it just short of perfect.

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?

There is no output schema, so the description carries the return-value burden, and it does flag the PII redaction (IP and coordinates removed), which is the key thing an agent needs to know about the response. It stops short of describing the full returned fields, but for a simple get-by-id tool this is close to complete.

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 subscriber_id parameter (its pattern, length bounds, and cross-reference to the list tool) is already fully documented. The description's 'by id' adds no syntax or format detail beyond the schema, 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+resource+scope: retrieves one calendar subscriber by id, distinguishing it implicitly from the list_calendar_subscribers sibling. However, it does not explicitly name the list alternative, so it stops just short of full sibling differentiation.

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 'One calendar subscriber by id' implies the single-record use case versus the list tool referenced in the schema, but there is no explicit statement of when to use this versus addevent_list_calendar_subscribers or other get_* siblings. Usage is only implied.

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