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

Goes well beyond the annotations: it explains that aliases canonicalize, that duplicate selections are deduplicated (reinforcing idempotentHint with mechanism), that existing prompt overrides remain unchanged yet may still select the region, how allowance is computed (distinct union of defaults and enabled overrides), and that it returns the complete scanConfig without launching a scan. This is rich side-effect and mutation 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?

Dense but front-loaded: the core add action leads, followed by behavioral details. Every sentence (canonicalization, dedup, override behavior, allowance, return value, no launch) adds distinct information, though the stacked clauses make it slightly heavy to parse.

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 mutating, non-destructive, idempotent tool, the description covers side effects, prerequisite source (list_regions), tool boundaries (no scan launched), and even the return payload. An output schema exists, so return-value detail is optional, yet the description still notes it, leaving nothing an agent needs to call it correctly.

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 coverage is only 50% (region is undocumented in the schema), so the description carries the burden and does add meaning: region is a canonical country/city ref drawn from list_regions and aliases are canonicalized. siteId is already documented in the schema, so the description correctly doesn't repeat it.

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 (add) and resource (selectable canonical country/city ref) and names the exact scope: Site/Topic scan defaults. It also distinguishes itself from siblings by sourcing the ref from list_regions and explicitly stating it does not launch a Scan, separating it from trigger_scan.

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?

Gives clear context: the ref must come from list_regions and is applied to scan defaults, and the closing 'Does not launch a Scan' implicitly routes the agent away from trigger_scan. However it never explicitly names remove_scan_region as the inverse operation, so the when-not guidance is only implied.

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