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

Annotations already declare readOnly and idempotent behavior; the description goes further by disclosing that the calculation is approximate, cashback expectations are site estimates, construction fees vary, and it explicitly reports if not switching is better. This adds meaningful limitations without contradicting annotations.

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?

The core functionality is front-loaded in the first sentence, and the second sentence explains the result behavior. The disclaimer paragraph is longer but contains essential caveats. No redundant fluff; every sentence contributes.

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 calculation tool with no output schema, the description explains the return value (total difference), behavioral handling when staying is better, and key limitations. Parameter coverage is fully handled by the schema. It could specify the exact output format more concretely, but overall it is sufficient.

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%, with each of the 8 parameters well-documented in the schema. The description groups penalty/construction/removal costs but does not add new semantic meaning beyond the schema's per-parameter descriptions, so 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?

The description clearly states a specific verb and resource: it returns the total cost difference between switching and staying, using current contract penalty/construction/removal costs and monthly fee. It distinguishes itself from siblings like search_hikari_plans (search) and compare_hikari_plans (comparison) by focusing on the switch-cost integration.

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: use when a user has current contract costs and wants a switching vs. staying comparison. However, there is no explicit guidance on when not to use it or which sibling to choose instead (e.g., simulate_hikari_cost). The disclaimer adds context but no selection criteria.

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