What changed

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description adds real value by disclosing the return structure: a summary paragraph, ranked findings with before/after values and onset times, evidence links, and per-signal coverage.

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 tight sentences, front-loaded with the core purpose before the return-value detail. The trailing imperative 'Start here.' is a useful orientation cue rather than waste, though it sits at the end rather than the front.

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 describing returns and does so thoroughly (summary, findings, coverage). Combined with fully documented parameters and annotations covering safety, an agent has nearly everything needed, though explicit routing to sibling tools is absent.

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 every parameter (since, until, service, baseline, budget_tokens) is already documented in the schema. The description's mention of 'baseline' and '(or all services)' overlaps with what the schema already states, adding no syntax or format detail beyond it.

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+resource ('what changed in a service... across metrics, logs and traces') and scopes it precisely with the baseline comparison. The 'Start here' framing positions it as the entry-point tool, distinguishing it from the drill-down siblings new_errors and trace_diff.

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?

'Start here' gives clear context that this is the workflow entry point, and 'Omit to scan every service' clarifies scope behavior. It stops short of naming when NOT to use it or routing to new_errors/trace_diff explicitly, so it lacks the full when-not/alternatives treatment of a 5.

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