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

Annotations only declare readOnly/openWorld/non-destructive; the description adds substantive behavior beyond them: browser rendering, anti-blocking capability, size reduction (2-25% of HTML), content stripping, link absolutization, and per-call billing. Those are exactly the facts an agent needs to predict cost and output shape.

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 what the tool does, then output characteristics, then usage and the competing sibling, then cost. Long but dense and every clause carries a distinct decision-relevant fact; no repetition of the title or name.

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?

For a single-URL fetch tool with no output schema, the description covers origin, rendering behavior, output format, failure modes handled, cost, and the alternative tool. Nothing needed to call it correctly 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 every parameter including wait_method, proxy_country, sleep_seconds and main_content_only is already documented in the schema. The description adds no parameter-level guidance (e.g. when to set wait_method or which country codes matter), so it sits at the baseline for a fully documented schema.

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 and resource ('Fetch a web page ... return it as clean Markdown') and defines the output shape precisely: main content, absolute links, no scripts/styles/nav/footer. It also names the sibling it is not (fetch_html) and the condition that selects it, so the agent can differentiate among siblings without opening 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?

Explicit when-to-use ('read, quote or summarise a page', JavaScript-rendered pages, 403/429/captcha walls) and an explicit alternative with its condition ('Use fetch_html instead when you need the markup, selectors or browser steps'). Also discloses billing as one request, which influences selection.

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