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

Beyond the readOnlyHint and openWorldHint annotations, the description discloses important behavior: parsing is inert, nothing loads, no tracking pixel fires, and no link is followed. It also warns that SURBL lookups consume the daily free limit, which is critical operational context.

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 front-loaded with the core action and outputs, then adds safety and quota context. Every sentence provides useful information without repetition or filler.

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 adequately lists what is returned: clipping-size analysis, link and image hosts, tracking pixels, URL shorteners, and SURBL results. Combined with annotations and schema, an agent has enough information to call the tool 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 coverage is 100%, so the schema already defines both parameters. The description adds meaningful semantics for scan by explaining that SURBL lookups consume the daily free limit and can be disabled, which goes beyond the schema's brief wording.

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: reading an email's HTML and returning size, link/image hosts, tracking pixels, shorteners, and SURBL checks. This is clearly distinguishable from sibling tools like analyze_headers or check_surbl, which operate on different inputs.

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 a clear usage rule for the scan parameter: SURBL lookups count against the daily free limit and can be skipped by setting scan to false. It does not explicitly compare this tool to alternatives such as check_surbl, but the intended context is clear.

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