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

Annotations already establish the safe read-only, idempotent profile, so the bar is lower. The description adds real value by disclosing the shape of the result: p75 percentiles, per-metric ratings, a period-over-period delta, and a worst-pages list, which tells the agent what it can conclude without a second call.

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?

A single dense sentence with the metric list and output content front-loaded, and no filler. The colon-plus-parenthetical construction is slightly compressed but still parseable in one pass.

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 no output schema, the description carries the burden of explaining return values and does so concretely (metrics at p75, ratings, delta, worst pages). The only gap is the absence of any scoping or default-range context, which the schema covers.

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 description coverage is 100%, so both 'range' (with its enum and 7d default) and 'project' are already documented in the schema; baseline 3 applies. The description contributes nothing about range semantics or project scoping, but nothing is lost either.

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 names a specific resource (web vitals: LCP, INP, CLS, FCP, TTFB) measured at p75 for real visitors, which is far more informative than the title alone. It does not explicitly contrast itself with the nearest siblings (relia_uptime for availability, relia_dashboard for aggregate views), so an agent must infer the boundary.

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?

There is no when-to-use or when-not-to-use guidance, no mention of alternatives such as relia_uptime, and no note that 'project' is only needed on multi-project tokens. The agent gets a topic, not a routing rule.

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