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

Annotations already cover read-only/idempotent/non-destructive, but the description adds substantially more: it reports ALL blockers rather than the first, deliberately does not claim an event count because it is not computed, a positive preview is not a reservation, a sync copies continuously rather than once, and it costs no credits. That is genuinely new behavioral context beyond the structured hints.

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?

Dense and front-loaded with the core purpose, and most sentences carry load (blockers, non-reservation, no credit cost). Minor cost: the defensive 'that is not computed, so it is not claimed' clause and 'A sync copies continuously, not once' add words that could be tighter, and the prerequisite paragraph stacks several constraints in one block.

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?

With an output schema present, the description need not explain return values, and it covers what matters: prerequisites, the max_detail_level/detail_level/reverse relationship, the fact that all blockers are returned, and the caveat that create_sync re-validates. Nothing needed 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 the baseline is 3, but the description adds real relational meaning: max_detail_level is the ceiling this access may copy, detail_level checks a specific level against it, and max_reverse_detail_level governs flow back for two-way. It also clarifies reverse_detail_level defaults to detail_level, which the schema only implies via $ref.

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 first sentence states a precise verb and resource ('Checks whether a sync ... could be created') and immediately bounds it with 'without creating anything,' which cleanly separates it from create_sync. The one-way/two-way enumeration further pins the scope and all 14 siblings are clearly not this tool.

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?

It names the alternative (create_sync) and explains the relationship, stating that the same checks run again on write and conditions can change. Prerequisites are spelled out (source shared with this access, target released via list_calendars: sync_target; both for two-way), which is exactly the when-to-use context an agent needs.

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