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

readOnlyHint=true already declares a safe read, so the burden is lower. The description adds the REST mapping (GET /subscriptions/{subscription_id}/usage), which is mildly useful context but discloses nothing about pagination, bucket limits, defaults when granularity is omitted, or rate limits.

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 compact sentences, purpose front-loaded, no filler. The endpoint reference is the only marginal line, but it is short and the whole definition is well under any bloat threshold.

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?

There is no output schema, so the description is the only place the return shape could be sketched (buckets, grouped rows, aggregation semantics), and it does not. For a 5-parameter, bucket-producing usage endpoint, the definition is adequate but leaves the agent guessing about what comes back.

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 all five parameters are already documented in the schema (ISO-8601 bounds, inclusive/exclusive, group_by, granularity). The description only echoes the timeframe concept, adding no format or default detail beyond the schema – the baseline 3 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 ('Get metered usage for a subscription') plus the scope ('over a timeframe'), which separates it from cost-oriented siblings like orb_get_subscription_costs. It stops short of explicitly naming a sibling to disambiguate against, so it lands at 4 rather than 5.

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?

Usage is implied by the resource itself (get subscription usage), and the 'over a timeframe' phrase hints that the timeframe params are expected. However there is no explicit when-to-use, when-not, or alternative named – notably no distinction from orb_get_subscription_costs or orb_get_subscription.

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