CountTool

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

With no annotations, the description carries the full behavioral burden, but it only states the return value. It does not disclose that this is read-only, how authentication is resolved across the many AWS/OpenSearch credential parameters, or what happens when no index or query is provided.

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?

A single sentence that is front-loaded with the operation and contains no fluff. It does not repeat schema details and earns its place by stating the tool's core behavior plainly.

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?

Although the schema richly documents parameters, the tool has 12 parameters, no annotations, and no output schema. The one-line description does not address how to form the query body, whether authentication is required, or what the count response looks like, leaving too much for the agent to infer.

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 high (92%), so the schema already documents the connection parameters and request body; the baseline of 3 applies. The phrase 'matching a query' adds slight meaning by implying the body should contain a query, but it does not explain query syntax or index/body interactions.

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 states a concrete operation ('Returns number') and a resource ('documents matching a query'), which distinguishes it from siblings like SearchIndexTool that return documents rather than counts. It does not explicitly name an alternative or endpoint, but the core 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?

Usage is implied rather than explicit: the description suggests this tool is appropriate when a count of matching documents is needed. However, it does not provide when-not-to-use guidance or mention alternatives like SearchIndexTool or MsearchTool.

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