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

Annotations already declare readOnly/idempotent/non-destructive/openWorld=false, but the description adds a real contract on top: invalid or missing input never raises a protocol error and instead returns {"error": "<what is wrong and how to fix it>"}, with a worked example. It also states retry is always safe after correction, which directly supports error recovery behavior.

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?

Front-loaded with purpose, then example, then usage and error semantics — good ordering with no filler sentences. It is somewhat long for a two-parameter validator, and the error-handling paragraph repeats the retry point twice, which trims it below maximum efficiency.

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?

Covers everything an agent needs: what it does, when to use it, what it does not do, the shape of success and failure returns, and cost ('FREE'). With an output schema present, the description need not explain verdict fields further, and it doesn't over-explain them.

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%, so the baseline is 3, but the description adds a concrete example input that shows the expected relative-path format ('my-skill/SKILL.md') and a marketplace value, plus the returned skill_files_found echoing matched skill paths. It does not, however, explain the marketplace rule-set tradeoff beyond restating what the schema already documents.

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?

States a specific verb+resource ('Validate a zip layout plan for a skill marketplace before packaging') with a concrete boundary: it checks layout, not skill content. It explicitly names the sibling it is not (lint_skill), so an agent can separate the two without inspecting schemas.

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?

Gives explicit timing ('Use on a planned file layout, before zipping') and an explicit exclusion pointing to the alternative ('Not for the content of a skill file (lint_skill)'). Both the when and the when-not are stated, leaving nothing to inference.

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