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

With no annotations supplied, the description carries the full disclosure burden and does a solid job: it reveals the billing model ('pay per check'), the stateful transition semantics ('new' on first call, then 'changed'/'unchanged'), and the returned fields (changes_since_first_seen, first_seen, last_checked). Gaps remain around what counts as a change (content hash vs. full page) and whether state survives across sessions or expires.

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?

One dense sentence (with an em-dash clause) that front-loads the core behavior and then enumerates the response states and fields. No filler, no restatement of the tool name, and every clause carries information the agent needs.

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 one-parameter tool with no output schema and no annotations, the description covers the essentials: what is monitored, that it is stateful and billed per call, and what the response contains. Only the state-persistence lifetime and change-detection semantics are left unstated, which are secondary for correct invocation.

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 required 'url' parameter with 0% schema description coverage, so the schema contributes nothing. The description's 'Watch a URL' supplies the basic meaning — the target to monitor — but adds no detail on accepted formats, redirects, or authentication-protected URLs, which is thin for the only parameter.

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 — watching a URL over time with recurring, stateful checks — which is meaningfully distinct from a one-shot fetch. It does not, however, name or contrast the closely related siblings (check_change, check_link), leaving the agent to infer the boundary from the 'call periodically' phrasing alone.

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?

'Call periodically and pay per check' implies the usage pattern and warns of a cost model, which is genuinely useful guidance. But there is no explicit when-not, no mention of the sibling check_change that likely covers similar ground, and no statement about how long monitoring state persists between calls.

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