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

Annotations already cover readOnly/idempotent/non-destructive and closed-world, but the description adds genuinely new limits (200k input, 150k output characters) and clarifies no network fetch occurs. Return format is carried by the output schema, so this is close to complete.

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?

Four short sentences, each doing distinct work: what it does, when to use, param caveat, limits. Front-loaded with the core action and the key disambiguation.

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?

An agent can decide and call correctly: mutation profile from annotations, return shape from output schema, limits and routing from the description. Only the truncation semantics of max_chars remain unstated.

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 0%, so the description must compensate: it explains base_url's role (resolving relative links) and states input/output character limits matching html.maxLength and max_chars.maximum. max_chars itself is not described as a truncation control, leaving a small gap.

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?

Specific verb+resource ('Converts supplied HTML into readable Markdown') plus an explicit negative scope ('without fetching a URL') that cleanly separates it from fetch_markdown, which is named directly.

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?

States exactly when to use it ('when the agent already has HTML'), names the alternative (fetch_markdown when Plainport should retrieve the page), and scopes base_url's narrower purpose.

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