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

Annotations declare the safety profile (readOnly, non-destructive, closed-world), and the description adds substantive behavior beyond them: the return is a PNG image content block plus a public URL, the URL allow-list is enforced both locally and by a host firewall, and private/internal hosts are rejected. That is exactly the extra context annotations cannot carry.

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?

Front-loaded with the scope constraint and organized into short, purposeful blocks with no filler. There is mild redundancy between the 'Non-DreamAgent URLs are rejected' line and the closing 'private/internal hosts are rejected' sentence, which keeps it from a perfect score.

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 no output schema, the description compensates by explaining what is returned (PNG image block plus public URL). Scope, required input, and rejection behavior are all covered, so an agent has everything needed to call it correctly.

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 description coverage is 100%, so all three parameters (url, width, height) are already documented with types, defaults and ranges. The description only reinforces the url requirement ('No project id needed — just the URL'), adding no new meaning for width/height, so the 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 precise verb (capture a screenshot) and a tightly scoped resource (a DreamAgent-hosted page by URL), opening with 'WEBSITE PROJECTS ONLY' so the agent can immediately distinguish it from sibling tools that touch source files or project metadata.

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 context for use ('Best for checking a project's live pages after edits or deploys and reviewing layouts') and clear exclusion rules ('Non-DreamAgent URLs are rejected'). It never names an alternative sibling (e.g. read_file for source inspection), so it stops short of full when/when-not/alternative coverage.

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