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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds meaningful context beyond that: the content is 'public' (implying no auth/paywall) and the return includes both metadata and body paragraphs. It stops short of disclosing rate limits or error behavior, so it's a strong but not exhaustive addition.

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?

Two sentences, zero waste. The fetch statement is front-loaded and the sibling routing follows compactly; every clause earns its place.

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?

An output schema exists, so return structure needn't be explained, and annotations carry the safety profile. The description fully covers what the tool does and when to prefer a sibling, so nothing an agent needs to call it correctly is missing.

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?

With a single parameter at 100% schema description coverage, the schema already documents 'Canonical www.npr.org article URL'. The description reinforces 'canonical url' but adds no format or validation detail beyond the schema, matching the baseline for well-covered params.

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 ('Fetch') and resource ('NPR article metadata and body paragraphs'), plus the exact input ('canonical url'). It is immediately distinguishable from npr_headlines, npr_topic, npr_categories, and npr_author, which it names.

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?

Explicitly routes the agent: npr_headlines for story lists, npr_topic for topic coverage, npr_categories to discover sections, npr_author for an author profile. Each alternative is paired with the condition that selects it, 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.