Audit page performance

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

Annotations already declare readOnlyHint/openWorldHint/idempotentHint, and the description adds meaningful context beyond them: this is a lab (headless Chromium) measurement, INP is only reported 'when actions interact', and results include rated verdicts against Google thresholds or custom budgets. It stops short of disclosing cost/runtime (each call launches a browser, so multi-run audits are slow) or that it requires a Playwright project context.

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?

Effectively one long sentence that front-loads the verb, the measured metrics, and the outputs before trailing capabilities, which is well adapted to a 20-parameter tool. It is dense and slightly run-on, and 'in headless Chromium' partially duplicates the browser parameter, but nothing is wasted.

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?

An output schema exists, yet the description still usefully previews what comes back (ratings, locators, request lists, budget verdict) and covers measurement conditions and the optional auth/mock/interaction inputs. It omits practical prerequisites (a Playwright project root, long runtimes for multi-run medians) that an agent would want before invoking it repeatedly.

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 90%, so the schema already carries the parameter documentation burden. The description calls out useful capability clusters (storageState/headers for auth, actions for reaching state, routes for mocking, throttled phone, median of runs), but it adds no syntax or constraint detail beyond what the schema already says. Baseline 3 applies.

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 ('Measure a page's lab Web Vitals') and enumerates the exact metrics plus the derived artifacts (LCP element locators, shifting elements, heavy/render-blocking requests, budget check). This is clearly distinguishable from siblings like audit-accessibility, inspect-page, and run-test.

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 mention of budgets and 'the spec' hints at CI/pre-ship gating and the throttled/median options hint at mobile profiles, but the description never says when to choose this over audit-accessibility or run-test, nor does it state prerequisites or exclusions. An agent must infer the fitting scenario.

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