dirname

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

Annotations already provide readOnlyHint=true, and the description reinforces this with 'Read-only, no side effects'. It adds behavioral context beyond annotations by specifying that it returns JSON with the directory path. However, it does not disclose potential errors or edge cases.

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 relatively concise at two sentences, but includes redundant statements like 'Read-only, no side effects' which are already covered by annotations. Could be slightly more streamlined.

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 that there is no output schema, the description compensates by describing the return format (JSON with directory path). It covers use cases, alternative tools, and behavioral flags, making it fully complete for a simple tool with good annotations.

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%, so the schema already fully describes both parameters. The description does not add meaningful information about the parameters beyond what is in the schema, such as format constraints or usage nuances.

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 it returns the parent directory portion of file paths, which is the core purpose. It distinguishes itself from the sibling 'basename' by specifying it strips the final component, while also referencing 'realpath'. This provides a precise and unique purpose.

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 explicitly tells when to use the tool ('extract directory prefixes from full paths') and when not to ('not for extracting the filename — use 'basename''). It also references an alternative tool ('realpath'), providing clear usage guidance.

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