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

Annotations already cover readOnly/idempotent/non-destructive, and the description adds genuinely beyond that: a hard stop date 12 months after launch, three emailed notices, and a migration doc mapping every call. The GDPR/PECR passage is behaviorally informative about audience composition (sole traders and ordinary partnerships excluded by default) but sits oddly on a filter-value lookup.

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?

Deprecation and the replacement are correctly front-loaded, but the legal-basis and PECR sentences consume roughly half the text and do not help an agent decide or call this tool. Sizing is disproportionate for a zero-parameter deprecated lookup.

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?

An output schema exists, so return values need no explanation, and deprecation/migration are fully covered. What is absent is how an agent obtains the numeric category id in the first place (the sibling available_selection_categories) and the exact deadline date rather than a relative one.

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?

Zero declared parameters, so the baseline is 4; the description still adds that the tool is addressed 'by numeric id' and that the adapter passes the old arguments through unchanged during the deprecation window, pointing to the migration doc. The reference to a 'toggle' for email audiences names a setting that is not a parameter of this tool, which is mildly confusing.

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 first sentence gives a specific verb and resource ('lists the values of one filter category by numeric id') and immediately flags deprecation, so an agent knows exactly what the tool returns. It is differentiable from search_filter_values, though the remaining two-thirds of the text dilute the signal rather than sharpen it.

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?

Explicitly routes the agent to search_filter_values and even describes that replacement's inputs and return shape, which is unusually strong for a deprecated tool. What is missing is the inverse case: no statement of when this tool remains the correct call (i.e. only inside the 12-month migration window).

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