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

Annotations already declare readOnlyHint=true, so the read-only nature is covered. The description adds useful behavioral context: it accepts both code and full URL, and it explains the ?md rendering behavior for Markdown. It doesn't mention rate limits or response format, but for a simple read tool with readOnlyHint, the description adds meaningful value beyond 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?

Three sentences, each earning its place: the first states the core function, the second clarifies input flexibility, the third gives a practical usage tip. No fluff or repetition of schema details.

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?

For a simple read tool with one parameter, full schema coverage, and readOnlyHint annotation, the description is nearly complete. It covers what the tool does, input formats, and a rendering tip. It doesn't describe the return format, but with no output schema and a simple text-fetch operation, that's a minor gap.

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 schema already documents the 'code' parameter well. The description adds value by clarifying that the parameter accepts either the 6-character code or the full URL, and by explaining the ?md suffix behavior. This goes beyond the schema's description, which only says 'the paste's code... or its full xi.pe URL'.

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 the tool fetches the text of an existing xi.pe paste, with a specific verb ('Fetch') and resource ('text of an existing xi.pe paste'). It also distinguishes itself from siblings by mentioning it can read pastes handed over by users or agents, and the sibling tools (create_paste, delete_paste) are clearly different operations.

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 says when to use it: to fetch an existing paste, including one just handed to you. It also provides a conditional usage tip: if passing the URL to a human and the text is Markdown, append ?md. It doesn't explicitly name alternatives, but the sibling tools are create and delete, so no alternative read tool exists; the usage context is clear.

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