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

Annotations already declare readOnlyHint and idempotentHint, covering safety. The description adds behavioral context: 'A small bounded catalog fetched live from OpenAQ' reveals that the tool performs a live fetch and returns a limited set, which is useful for planning. It also notes the default behavior for pollutantsOnly via the parameter, but that is schema-covered. No contradictions with annotations; the added info is valuable but not extensive.

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 three sentences with zero fluff. It leads with the tool's core function (catalog of pollutants and units), then explains purpose and usage, and ends with a note on the bounded live fetch. Every sentence earns its place, and the critical unit-disambiguation point is front-loaded.

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 simple-list tool with a rich output schema, the description is complete. It covers the tool's output content (fields), the filtering parameters, the use cases, and the bounded nature. It does not need to describe return format because the output schema defines it. There are no obvious gaps an agent would need to know 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 description coverage is 100%, so the baseline is 3. The description does not add new parameter meanings beyond what the schema already provides: the query parameter's filtering behavior and the pollutantsOnly flag are both fully documented in the schema with examples and defaults. The description reuses the same information without extension, so no extra semantic value is added.

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 clearly states the tool lists a catalog of pollutants with canonical units, specifying the exact fields (id, code, display name, unit, description). It distinguishes itself from siblings like openaq_list_countries by focusing on pollutant parameters and unit disambiguation, and it explicitly mentions the sibling tools (openaq_find_locations, openaq_get_readings, openaq_get_measurements) that it supports. Purpose is unambiguous.

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 gives explicit when-to-use guidance: 'use this to pick the exact parametersId for openaq_find_locations / openaq_get_readings / openaq_get_measurements and to interpret a reading's unit.' It also indicates that omitting the query lists everything, which clarifies a common usage. It does not explicitly state when not to use it or name alternatives to avoid, but the context is strong enough to route an agent correctly.

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