get_index_stats

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

With no annotations, the description carries the full burden and does disclose two meaningful traits: it is fast and it does not trigger vector store initialization, which implies no expensive side effects. It stops short of stating read-only status or cost/limits explicitly, but 'Returns statistics' makes the non-mutating nature clear.

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?

Two short sentences, result stated first, the performance caveat second. No filler, no restating of the tool name, and the most decision-relevant fact (it's cheap) is front-loaded after the 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?

An output schema exists, so return values needn't be described, and with zero parameters the input side is trivially complete. The description covers purpose and cost profile adequately; only the relationship to sibling inspection tools (index progress, cache stats) is left unaddressed.

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 tool takes zero parameters, so the baseline is 4; there is nothing for the description to disambiguate. The parenthetical hint at what the returned statistic is adds a small amount of direction without duplicating the schema.

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?

States a specific verb and resource: 'Returns statistics about the current vector store (number of chunks).' An agent can tell this is a read-only inspection call, but it never distinguishes itself from nearby siblings like get_index_progress or get_cache_stats, which could plausibly return overlapping information.

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?

'This operation is very fast and doesn't trigger vector store initialization' implicitly signals a cheap, safe pre-check, but there is no explicit when-to-use statement and no named alternative (e.g., use get_index_progress while indexing is running). Usage must be inferred.

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