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

Annotations declare readOnlyHint=true and openWorldHint=false, so safety is already covered. The description goes beyond that by describing the response contents (names, emails, per-person rotation, escalation policies), which is real value given there is no output schema. It does not mention failure modes when `at` falls outside the 90-day window, so it stops short of a 5.

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?

Two sentences, front-loaded with the core question it answers, followed by the routing instruction. Dense but every clause carries information; the parenthetical example is justified because it teaches the accepted input form.

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 read-only, single-optional-parameter tool with no output schema, the description covers purpose, timing semantics, returned fields, and usage routing. Only the out-of-range/error behavior for `at` is left unstated, which is a minor gap since the schema documents the 90-day bound.

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 schema documents the ISO 8601 format and the 90-day limit, so baseline would be 3. The description adds meaning the schema lacks: it accepts natural-language moments like 'next Saturday 10:00', and clarifies the default behavior is 'right now'. That is a genuine semantic addition.

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 resource (who is on call) with a precise temporal scope (right now or at the time in `at`), and names the computation source (the engine that pages people). The description also lists the returned entity types (names, emails, rotation, escalation policies), which lets an agent distinguish it from get_on_call_schedule and list_on_call_schedules without opening a schema.

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?

Explicitly routes the agent: 'Use it for any "who is on call" question instead of reading rotation rules.' That names a when-to-use and an alternative approach. It does not, however, contrast itself with the sibling tools get_on_call_schedule or list_on_call_schedules, which is the more likely confusion point.

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