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

Annotations already establish read-only/idempotent behavior. The description adds value by disclosing the exact response shapes for each format and the deterministic nature of facts, which is beyond annotation coverage. No contradiction.

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?

Three compact sentences, front-loaded with the verb+resource, and every clause adds functional detail (format behaviors, response shapes, example). No fluff.

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 simple 2-parameter schema and idempotent/read-only annotations, the description fully covers expected behavior for all three formats, including return shapes. No output schema is present, so this return-shape documentation is essential and sufficient.

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?

The schema covers 100% of parameters, so baseline is 3. The description goes beyond schema by spelling out return objects for each format and giving a concrete fact example, though it does not add much to the 'source' parameter beyond schema.

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 a specific verb and resource ('Describe a Mermaid diagram') and the format parameter clarifies three distinct output modes. This clearly differentiates from siblings like describe_sdk and render_*.

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 gives clear format-specific use context (e.g., facts for machine checking) but never explicitly states when to choose this tool over sibling tools such as render_* or verify. Usage is implied rather than directly contrasted.

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