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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering safety. The description adds value by disclosing the exact return contents (title, image URL, alt text, date, transcript, permalink), which goes beyond annotations and helps the agent set expectations. No contradiction with annotations.

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?

A single, focused sentence that front-loads the core action and resource, then efficiently lists the return fields. Every word earns its place, and there is no redundant or vague phrasing.

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?

This is a simple one-parameter tool with a clear description, a complete input schema, output schema, and annotations that declare it safe and idempotent. The description covers purpose, parameter, and return content, so it is fully complete for an agent to select and invoke this tool correctly. Minor sibling differentiation gaps are captured in the usage_guidelines dimension.

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 input schema already describes the 'number' parameter thoroughly (type, examples, and meaning), giving 100% coverage. The description reinforces this with a concrete example ('353 for \'Python\'') but adds no new syntax or constraints beyond the schema, so it is at baseline.

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 uses a specific verb ('Fetch') and clearly identifies the resource ('a specific XKCD comic') with the key differentiator 'by its number'. It also lists the returned fields, making the purpose unambiguous and easily distinguishable from sibling tools like random_comic or get_latest.

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 clearly implies when to use this tool: when you have a specific comic number in mind. However, it does not explicitly name alternatives or state when not to use it (e.g., use random_comic for a random comic, get_latest for the most recent). Despite this, the context is clear enough for basic selection.

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