Start a timer helper

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

Annotations already declare readOnlyHint=false, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds a genuine behavioral nuance not in the annotations: calling it on an already-running timer restarts it with the new duration. It also notes the underlying `timer.start` HTTP call, though the return behavior it mentions is already covered by the output schema.

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?

Front-loaded with purpose, then Use-when / Not-for / Returns structure that is easy to scan. The HTTP/`timer.start` implementation detail is slightly more than strictly needed but does not bloat the definition.

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 2-parameter timer tool with full schema coverage, an output schema, and annotations covering the safety profile, the description supplies the remaining useful context (override semantics, restart behavior, when to use it). Nothing an agent needs to call it correctly is missing.

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 entity_id and duration (including format and the omit-to-reuse-configured-duration default) are already fully documented by the schema. The description confirms the two parameters are passed but adds no syntax or format detail beyond that, so 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?

Specific verb+resource ("Start a timer helper, optionally overriding its duration") with the exact semantics of the override and restart behavior. It also names the sibling it is not (helpers_cancel_timer), so an agent can distinguish it without opening the 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?

Explicit "Use when: starting a countdown... Not for: stopping it early — use `helpers_cancel_timer`." Both the positive case and the exclusion with an alternative are given, leaving nothing to inference.

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