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 a genuine behavioral detail beyond them: it follows redirects, which tells the agent that a bare 3xx is not a failure and that a network round-trip occurs. It does not say what a failed resolution returns, but the output schema covers return values.

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?

One short sentence that front-loads the action and constraint with zero filler. Nothing in it is redundant with the title or schema.

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?

With rich annotations, an output schema, and fully documented parameters, the description only needs to convey purpose and timing, and it does. The minor gap is not stating how an unresolvable URL is surfaced versus thrown, though the output schema likely handles that.

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?

There is a single parameter with 100% schema description coverage, so the schema already specifies that a full https://unpkg.com/... file URL is required. The description only implies the same constraint and adds no format, encoding, or scoping detail beyond it.

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 ('Check that a UNPKG file URL actually resolves'), which distinguishes it from siblings like build_file_url or resolve_package that construct or inspect rather than verify liveness. It does not name any sibling explicitly, so differentiation is inferred rather than stated.

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?

'before you put it in a project' gives a clear timing cue for when to reach for this tool, which is more than a bare purpose statement. It stops short of explicit exclusions or naming the alternative (e.g., build_file_url for constructing the URL first), so an agent must infer that this is a post-construction check.

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