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

The description claims 'Inputs: target finish time, distance km,' but the input schema only includes 'target_time_minutes' with no distance parameter. This is a major contradiction between the description and the schema, introducing misleading information. No annotations exist, so the description carries the full burden, and it fails.

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 three sentences long, front-loaded with the tool's purpose and usage. It is appropriately sized and does not contain unnecessary information, though the incorrect mention of inputs slightly detracts.

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?

The description mentions return values (5K splits, halfway, final pace), which is helpful. However, it omits the fact that the input schema does not include distance, and it provides no information about the output schema's structure or possible edge cases. For a simple tool, this incomplete and partly incorrect context is insufficient.

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 coverage is 100% (one parameter with a description), so baseline is 3. However, the description adds a spurious parameter (distance km) not present in the schema, creating confusion. It does not enhance the understanding of the actual parameter beyond the schema's own description.

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 'Generate target split times for a marathon, half-marathon, or other race.' It clearly identifies the verb (generate) and resource (target split times for races), making the purpose evident. However, it does not explicitly differentiate from sibling tools like calculate_running_pace or calculate_race_prediction, though it suggests using list_bundles for related calculators.

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 says 'Use for race-day pacing,' providing a clear context of use. It also refers to list_bundles for related 'sport' calculators, implying alternatives exist, but it does not specify when to use this tool versus those alternatives or any exclusions.

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