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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so safety is covered. The description adds genuinely useful behavior the annotations do not: it refuses private/local addresses and caps the response at 800 KB. It does not disclose rate limits or that the page is fetched without JS rendering, but the added constraints are real value beyond structured fields.

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?

Three short sentences, zero waste, with the core action and return shape front-loaded and the two limits (address restriction, size cap) following. Every sentence carries independent information.

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, the description needn't detail return values, and annotations cover the safety profile; the description fills the remaining gaps (address policy, size cap). Only minor omissions remain, such as whether JavaScript-rendered content is fetched or how failures are reported.

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?

There is a single parameter with 100% schema description coverage, and the schema already states 'Public http or https URL. Private and local addresses are refused.' The description repeats that same constraint rather than adding format, redirect, or query-string semantics, so baseline 3 is appropriate.

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 (fetch) and resource (a public HTML page), plus the exact transformation (article to Markdown) and the accompanying outputs (title, excerpt, token count). This is clearly distinct from siblings like check_http_headers or validate_sitemap, which inspect rather than extract content.

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?

Scope is implied by 'public HTML page' and by the private/local refusal constraint, so an agent can infer when this applies. However, there is no explicit when-to-use statement, no mention of alternatives (e.g. extract_pdf_text for PDFs, check_robots_txt for crawl policy), and no prerequisites named.

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