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

The readOnlyHint annotation already marks it as read-only, but the description adds crucial behavioral context: the screenshot is taken at build time, not now, and a fresh one does not appear instantly after a publish. It also warns about the high context cost of images. These are behavioral traits not derivable from annotations alone.

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?

The description is well-structured: purpose in the first line, then complementary relationship, then timing warning, then cost advice. Each paragraph earns its place, though it could be slightly tighter. The key warnings are front-loaded after the purpose.

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 single-parameter read-only tool with full schema coverage, the description fully covers purpose, usage context, timing behavior, and cost trade-offs. Nothing an agent needs to invoke 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?

The schema already provides 100% coverage of the single `project` parameter, including accepted formats (slug, id, or URL) and the caveat that the address host is not always the slug. The description adds no parameter-level information beyond the schema, so baseline 3 applies.

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 states a specific verb and resource: 'A screenshot of the latest built version of the site — how it looks.' It explicitly differentiates from sibling tools by naming the complementary questions read_site and site_issues answer, so an agent can immediately tell what this tool is for.

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?

It gives clear when-to-use ('Useful before and after a visual change') and when-not-to-use ('Do not call it "just in case"') guidance, and explicitly routes the 'what is wrong' question to site_issues as cheaper and more specific. This is exemplary usage guidance.

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