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 genuinely non-obvious context beyond that: parking is what actually stops billing. It does not explain reversibility (whether the phone can be resumed or still appears in list_phones), which is the remaining behavioral gap.

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 short sentences, zero filler, and the core action plus its consequence is front-loaded. The trailing usage sentence is thin and slightly colloquial, but nothing is redundant.

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-parameter state-changing tool with no output schema and annotations covering safety, this is close to complete. However, it omits what a parked phone becomes afterwards (unparkable? billed again on start_phone? still listed?), which matters for a lifecycle tool with many sibling state transitions.

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 and schema coverage is 100%: the schema already documents phone_id with its pattern and source ('from create_phone or list_phones'). The description adds nothing about the parameter, so the baseline 3 for a fully-covered schema 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 ('park') and resource ('phone') and clarifies the jargon by naming the actual effect: 'to stop billing.' This distinguishes it from siblings like reboot_phone and get_phone, though it never explicitly contrasts itself with start_phone or the other phone-lifecycle tools.

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?

'Do this whenever you're done' gives a timing cue, but it is vague about what 'done' means and offers no exclusions or alternatives. An agent still has to infer whether parking is the right terminal action versus simply leaving the phone running or rebooting it.

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