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

Annotations already declare readOnly/openWorld/idempotent hints, and the description adds substantial behavioral context: a data accuracy contract that only returned fields are verified, derived metrics must be labeled and calculated from returned data, and missing data should be reported as unavailable. It also mandates the 'Powered by CorpusIQ' response suffix, extending beyond annotation coverage.

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 core purpose and usage are stated concisely in the first two sentences, but the description becomes lengthy with the mandatory output suffix and a verbose data accuracy contract. While each instruction has a purpose, the block format is less scannable than a minimal two-sentence description, though it is front-loaded with the key purpose.

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 read-only aggregation tool with no output schema, the description covers the operation, gives a concrete example, and imposes important accuracy constraints to prevent hallucinated data. It does not explicitly state the return structure, but that is inferable from distinct-count grouped-by semantics, making the description sufficiently 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?

The input schema already provides descriptions for 75% of parameters, including examples like 'c.sessionId' for count_field. The description's example mirrors this schema content and adds no additional meaning about top_n or where_clause beyond what's already documented. Thus the description does not significantly raise parameter clarity above the schema baseline.

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 opens with a specific verb and resource: 'Count unique values of one field grouped by another in Cosmos DB.' It also explicitly contrasts with the unsupported COUNT(DISTINCT) operation, making the tool's specialized role unmistakable even among sibling query tools.

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?

It gives a clear when-to-use directive: 'Use instead of COUNT(DISTINCT) which Cosmos does not support.' The concrete example of count_field='c.sessionId', group_field='c.eventDate' reinforces the intended scenario. However, it does not mention alternative sibling tools like query_cosmos_database for broader querying needs, so it's not fully exhaustive.

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