List indices

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

Annotations already declare readOnlyHint=true, so the description adds value by disclosing the fallback behavior to _resolve/index API when monitor privilege is absent. This goes beyond the structured data. No contradictions with annotations.

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 long, front-loaded with the core purpose, and includes essential fallback behavior. Every sentence is necessary and there is no waste.

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?

Given the tool's simplicity (one optional parameter, no output schema, readOnlyHint annotated), the description fully covers what the tool does, what it returns, and a key behavioral edge case. Nothing is missing for an agent to use 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?

The input schema has 100% description coverage for its single optional parameter 'index', describing it as an optional name or pattern for filtering. The description adds no additional parameter semantics beyond restating the schema, so baseline 3 is appropriate.

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 verb 'List indices' and specifies the returned fields: health, status, document count, and size. It also explicitly equates the tool to '_cat/indices', making the purpose unambiguous. This distinguishes it from sibling tools like cluster_health which focus on cluster-level metrics.

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 a clear context for when to use this tool, noting that it falls back to a name-only API when the cluster monitor privilege is missing. This implies it works even with limited permissions. However, it does not explicitly state when NOT to use it or name specific alternatives among siblings, hence not a 5.

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