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

readOnlyHint=true already tells the agent this is a safe read. The description adds the underlying endpoint (GET /subscriptions/{subscription_id}/costs), which is mild extra context but says nothing about aggregation behavior, default timeframe, pagination, or response size for what is clearly a reporting/aggregation call.

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, front-loaded with the purpose and no filler. The endpoint citation is marginally useful for API-savvy callers but borders on redundancy with the tool name.

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 should carry some sense of what comes back (cost breakdown by price, periodic vs cumulative series), and it does not. Parameters are well covered by the schema, but the return-shape gap leaves the definition only minimally adequate.

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 each of the 5 parameters is already documented (group_by, view_mode enum, timeframe bounds, subscription_id). The description adds no syntax, default, or interaction detail (e.g., how group_by and view_mode combine), so 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 and resource ('Get costs for a subscription over a timeframe'), so the agent knows exactly what it returns. It never names the closely related sibling orb_get_customer_costs, so the subscription-vs-customer distinction is left to inference even though it's the most likely confusion.

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?

No when-to-use guidance, no prerequisites, and no comparison to orb_get_customer_costs or orb_get_subscription_usage, which are the obvious alternatives. Usage is only implied by the resource name.

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