aggregate

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the agent knows this is a safe read operation. The description adds minimal behavioral context beyond this - it doesn't mention performance characteristics, result format, or error conditions. However, it doesn't contradict the annotations, so it earns a baseline score for adding some operational context.

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, efficient sentence that states exactly what the tool does with zero wasted words. It's appropriately sized for a tool with good schema documentation and gets straight to the point without unnecessary elaboration.

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 complexity (aggregation operations can be sophisticated), the absence of an output schema, and the rich annotations, the description is somewhat minimal. It adequately identifies the tool's purpose but doesn't provide guidance on result formats, error handling, or practical constraints beyond what's in parameter descriptions. It's complete enough to understand what the tool does but not how to use it effectively.

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?

With 100% schema description coverage, the input schema already thoroughly documents all parameters. The description doesn't add any meaningful parameter semantics beyond what's in the schema - it doesn't explain aggregation pipeline structure, database/collection relationships, or practical usage examples. Baseline 3 is appropriate when the schema does the heavy lifting.

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 action ('Run an aggregation') and target resource ('against a MongoDB collection'), which is specific and unambiguous. It distinguishes itself from simpler query tools like 'find' by specifying aggregation operations, though it doesn't explicitly differentiate from all siblings like 'explain' or 'export'.

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 clear context for when to use this tool (for aggregation operations on MongoDB collections). It also includes an implicit alternative in the parameter description (suggesting using 'export' instead if the entire result is needed), though this guidance isn't in the main description text itself and doesn't cover all sibling alternatives comprehensively.

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