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

Goes well past the annotations: discloses HTML escaping unless allowHtml, removal of javascript:/vbscript:/data: URLs, the 200 KB input cap, and the billing model ($0.002 per successful call via x402, failures not charged) — all decision-relevant. One tension: it asserts 'no outbound request' while openWorldHint=true is declared; the description is the more trustworthy of the two, but the mismatch is worth noting rather than treating as a contradiction of a readOnly-style safety claim.

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 dense sentences, front-loaded with the conversion and its outputs before the security, limits and pricing facts. Nearly every clause earns its place; the output-feature list is slightly run-on, which keeps it just under maximum.

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 an output schema present, return values need no explanation, and the description still covers the items that matter for correct invocation: size limit, escaping/sanitization semantics, determinism, and payment. Nothing an agent needs to call this successfully 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?

Schema coverage is 100%, so baseline is 3, but the description adds meaning the schema does not carry: which features gfm actually enables (tables, strikethrough), what headingIds produces, and the sanitization rules applied to links and images. It stops short of mapping every flag by name, leaving the schema to do the final binding.

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+resource (Markdown to HTML) and enumerates the exact output surface: GFM tables/strikethrough, heading ids, headings and links lists, and a word count. That detail separates it cleanly from neighbours such as text_readability, text_outline or encode without the agent needing to diff schemas.

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?

Usage is only implied: the agent can infer 'I have Markdown, I want HTML'. The 'pure code, no outbound request' line hints at when privacy matters, but no alternative sibling is named and there is no explicit when-not guidance. Adequate but leaves routing to inference.

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