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

Annotations already flag destructiveHint=true and idempotentHint=false; the description goes well beyond by explaining WHY (metered channels bill per use in USD, hence confirmation-gated), the allocation-vs-purchase distinction for shared channels, the preview-then-confirm mechanism, and the country-coverage validation that runs before creation. This is exactly the behavioral context an agent needs for a billing-affecting mutation.

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 the core action, then layers the constraint, billing rationale, and coverage pre-check in a logical order; every sentence carries information. It is a dense paragraph and slightly long, but no sentence is filler.

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 no output schema, the description still states the return ('created group id and key attributes, or a readable error'), covers all six parameters' semantics, the confirmation flow, and the billing/destructive implications. 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 the baseline is 3, but the description adds real meaning beyond the schema: the interaction constraint that at least one of shared/metered must be > 0, that amounts are in USD, and that country_iso triggers a pre-creation coverage check. The 'count not boolean' semantics are in the schema, so this is additive but not exhaustive.

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 and resource ('Create a Shared Capacity Group') and scopes it precisely ('inside one of the customer's Capacity Pools'). This clearly distinguishes it from create/update/delete/assign siblings like update_capacity_group and assign_did_to_capacity_group without needing to open any 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?

Gives explicit preconditions (provide name + capacity_pool_id, at least one channel count > 0), describes the confirmation-gated two-step flow, and routes the agent to list_capacity_pools for covered_country_isos and to the existing-group update path ('raising metered_channels_count on an existing group has the same effect'). When and how to use it is fully specified.

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