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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and closed-world, so safety is covered structurally. The description adds non-obvious behavior the annotations cannot convey: omitting the client parameter changes the result set entirely into a lateness ranking across all active Clients, and each result carries a one-line summary. It stops short of noting result volume, ranking method, or ordering of the per-quarter entries, so it is strong but not exhaustive.

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 sentences, front-loaded with the core return content, then labeled 'Use this when' and 'Not for' sections that scan instantly. No filler or restatement of the name; the dash-separated clause packs the measurement detail without bloat.

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?

There is no output schema, so the description must carry return-value semantics, and it does: quarter-by-quarter chase outcomes, lateness magnitude and direction relative to the requested date, an HMRC-deadline flag, and a summary line. Combined with a fully documented single parameter and complete annotations, an agent has everything needed to select and call it correctly.

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% and the single parameter is documented (name, email, or own reference), so baseline is 3. The description earns above baseline by explaining the semantic consequence of the optional parameter being absent — the call pivots from per-client history to a cross-client lateness ranking — which the schema alone cannot tell an agent.

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 the specific resource (a Client's Chases), the grouping axis (across Quarters), the exact measures returned (days early or late vs. the requested date, and vs. the HMRC deadline) plus a one-line summary. It also states the no-argument fallback behavior (every active Client ranked by usual lateness), which no sibling name implies, so an agent can distinguish it from whos_outstanding and list_clients without reading 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 routing is given: 'Use this when: asked whether a Client is usually late, how they did last time, or who's always late.' A negative case is also stated — 'Not for: who hasn't sent records this Quarter (whos_outstanding)' — naming the exact sibling to prefer instead. Both the when and the when-not are covered.

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