index_stats

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

With no annotations, the description carries the full burden for behavioral disclosure. It explicitly labels the operation as [READ], indicating safety, but does not mention potential performance impact, permissions, or whether it scans all indexes. The minimal disclosure is insufficient for a tool that may be invoked on large databases.

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 extremely concise and well-structured, with the [READ] tag leading, then a clear purpose statement, and a brief parameter explanation. Every sentence adds value without any redundancy.

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 is simple with one optional parameter and no output schema. The description conveys what the tool returns (column lists and cardinality) and the target parameter. It does not specify return formatting or any caveats, but for a read-only diagnostic tool, this is reasonably 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 has zero description coverage, but the description compensates by explaining the 'target' parameter as a target name from config that can be omitted for the default. This provides meaningful semantics beyond the schema's bare type definition.

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 returns per-index column lists and cardinality, with the purpose of selectivity screening. Although it lacks an explicit verb, the [READ] prefix and specific resource (indexes) make the purpose unambiguous and distinguish it from sibling tools like unused_indexes or redundant_indexes.

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 phrase 'selectivity screening' provides clear context for when this tool is appropriate, implying it is for examining index cardinality to assess selectivity. It does not explicitly list exclusions or compare to alternatives, so it stops short of a 5.

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