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

With no annotations, the description fully discloses a critical behavioral quirk: the API silently truncates to two areas for free callers, and the tool reports dropped areas in `locked`. It also instructs the agent to communicate this to the user, which is excellent transparency beyond the schema.

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 two sentences: the first states the purpose concisely, the second explains the limitation and correct usage. No wasted words; all content earns its place.

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?

The tool has no output schema, but the description covers purpose, input types, benchmarks/percentiles, and the critical truncation behavior with `locked`. It could detail the full return structure, but for a comparison tool with clear examples, this is sufficient.

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 100% with both `places` and `year` described. The description's 'Accepts names or codes' duplicates the schema's parameter description and adds no additional meaning. Therefore, the parameter semantics are adequate but not enhanced.

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 purpose: 'Side-by-side statistics for several Finnish postal areas, with national benchmarks and percentiles.' It clearly differentiates from siblings like get_place_stats (single area) and rank_areas (ranking) by emphasizing comparison of multiple areas.

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 description provides clear context: it's for comparing multiple postal areas and accepts names or codes. It also gives an important usage constraint (free callers are limited to two areas) and instructs the agent to acknowledge dropped areas. However, it does not explicitly name alternatives or state when not to use this tool.

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