time_start_timer

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

With no annotations, the description carries the full burden and does disclose one behavioral trait not in the schema: the 422 error on running/stopped timers. However it says nothing about auth requirements, billing/time-tracking side effects, or whether the operation is idempotent, leaving notable gaps for a mutation tool.

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, zero filler, with the action and the valid starting states front-loaded and the failure condition as a compact trailing caveat.

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 single-param timer-start tool with no output schema, the description covers the action, the valid states, and the primary error condition. Missing only peripheral details like auth or downstream effects, which are minor at this complexity.

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?

Only one parameter (id), and schema description coverage is 100% with the field documented as 'Timer ID'. The description adds no syntax or semantic detail beyond the schema, so the baseline 3 for schema-covered params 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+resource ('Start a timer') and even splits the two valid starting states (never run vs paused), which distinguishes it from pause/stop siblings. It doesn't explicitly name time_pause_timer or time_stop_timer, but the state-based framing makes the distinction inferable.

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?

The 422 caveat ('already running or stopped') effectively defines when this tool will not work, giving an agent a clear precondition. No alternative tool is named for those failure cases, so it falls short of explicit routing but still provides actionable context.

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