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

Annotations already declare readOnly, idempotent, non-destructive, so safety is covered; the description adds genuinely new context the annotations can't express — the cost model (free vs $0.001) and the fact that output is truncated to 500 characters, which is critical to know before relying on it for extraction. It stops short of describing rate limits or fetch failure 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?

Two sentences, zero filler, with the cost/limitation signal ('Free') front-loaded and the alternative named immediately after the capability. Every clause carries decision-relevant information.

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 one-parameter read tool with no output schema, the description enumerates the returned fields and the truncation boundary, which is exactly what an agent needs to judge whether the preview suffices. Nothing material 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?

Single `url` parameter with 100% schema description coverage ('Public http(s) URL', 4–2048 chars), so the schema already carries the semantics. The description contributes nothing parameter-specific beyond implying a public URL, which lands at the baseline 3 for high-coverage schemas.

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 and resource (fetches a URL) plus the exact return shape: title, metadata, outline, word/token counts, and the first 500 characters of Markdown. It also names the sibling it is not (read_url for full text), so an agent can separate the two without opening 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?

Explicitly routes the agent: use this free preview, use read_url (paid, with a concrete price) when the full text is needed. That is a clear selection rule. It doesn't address the read_urls batch sibling, but the core either/or decision is spelled out.

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