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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the agent knows this is a safe read operation. The description adds the 'aggregate' and 'over a specific period' scoping, which is useful. However, it doesn't mention any additional behavioral details such as return format aggregation level, or performance implications. Given the annotations cover the safety profile, the description adds modest value beyond the structured data, so a score of 3 is appropriate.

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 a single sentence that is concise and front-loaded with the usage trigger. It earns its place by providing the primary use case. It could have been slightly more explicit about the output being aggregates, but it's efficient and appropriately sized.

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 low complexity (1 optional parameter with enum), full schema coverage, and presence of an output schema, the description is sufficient to complete the tool's documentation. The output schema likely explains the return structure, so the description doesn't need to. The only minor gap is explicit differentiation from get_signal_details, but overall the tool is adequately 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?

Schema description coverage is 100% (the only parameter 'period' is fully documented with enum and default). The description mentions 'specific period' but doesn't add format or usage details beyond the schema. The baseline for full coverage is 3, and the description doesn't meaningfully exceed it. The parameter is simple and self-explanatory from the enum values.

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's purpose: retrieving aggregate AI signal performance statistics for a specific period. It uses a specific verb-resource combination ('get ... signal performance statistics') and is distinguishable from siblings like get_signal_details (which likely returns individual signal details) and get_signals (which likely lists signals). However, it doesn't explicitly name a sibling alternative when to use another tool, so it doesn't maximize differentiation.

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 begins with explicit guidance: 'Use this when the user asks for aggregate AI signal performance statistics over a specific period.' This clearly tells the agent the trigger condition. It doesn't specify when not to use it or name alternatives like get_signal_details for individual signals, but the context is clear enough for an agent to select it appropriately.

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