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

Though annotations already declare idempotentHint=true and destructiveHint=false, the description goes well beyond them: it explains the actual idempotency semantics (same currency+interval is replaced, other prices preserved), the DECISION_NEEDED no-op outcome when currency is ambiguous, and that the tool returns the full plan. This is genuinely load-bearing behavioral context the structured fields do not carry.

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 and idempotency model, then arguments, then the sibling pointer, then the guide pointer. Dense and mostly waste-free, though the trailing get_integration_guide sentence is only loosely tied to invoking this tool and the currency rule is restated in both the prose and the argument list.

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 mutation tool with 5 params and no output schema, the description covers the mutation semantics, the multi-currency decision path, the error-style outcome, deletion routing, and the return value ('Returns the full plan'). Nothing an agent needs to call this 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 coverage is 100%, so baseline would be 3, but the description adds value beyond the schema for currency: it spells out the multi-currency disambiguation rule and the resulting DECISION_NEEDED behavior, and restates amount>=0 and the interval choices in prose. It slightly duplicates the schema's currency note, which keeps it from a 5.

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 ('Add or update a recurring price on a plan') and immediately scopes it against siblings by naming remove_plan_price for deletion and by framing the operation as keyed on currency+interval. An agent can distinguish this from update_plan or set_plan_quota without opening 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 when-to-use ('add or update a recurring price'), the alternative for the opposite operation (remove_plan_price to delete), the condition for omitting currency, and a chained follow-up (call get_integration_guide with topic=billing before writing consuming app code). Nothing is left to inference.

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