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

With no annotations, the description fully carries the burden of behavioral disclosure. It transparently states that at most one timer runs per user and starting a new one replaces old ones, which is critical for a mutation tool. Missing details on auth or errors, but the key side effect is well communicated.

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?

The description is three sentences, with the most important action and side effects front-loaded. The sentence 'Supply subtask_id.' is a bit terse but clear. No unnecessary words.

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?

Given the tool has no output schema and 3 parameters, the description covers the core behavior: start/replace, lifecycle, and required input. It could mention what the tool returns (e.g., timer ID), but the current completeness is adequate for a single-action timer tool.

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 the baseline is 3. The description adds minimal value beyond the schema: it repeats 'subtask_id' and notes that description is optional. The idempotency_key is already well described in the schema.

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 clearly states the tool's action ('Start or replace your running timer') and resource ('on a subtask'). It also distinguishes it from sibling tools like stop_timer and cancel_timer, providing a specific verb+resource combination.

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 description explains the lifecycle: starting a new timer replaces any existing, and directs to stop_timer or cancel_timer for subsequent actions. It does not explicitly mention prerequisites or when not to use, but provides clear context for timer management.

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