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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds substantial behavior: 'HEAVY tool' cost warning, transport-specific capture rejection with a structured error, and the not_representable fallback shape at extreme inputs. These are non-obvious failure and cost characteristics an agent could not infer from annotations or schema.

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-loads the disclaimer and the core question well, but the output-mode paragraph duplicates material already spelled out in the envelope schema (summary/inline/capture and the stdio-only capture restriction), adding length without new information. The most useful edge-case detail (not_representable) is buried at the very end.

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 carries the full burden and does so: it names the echoed response fields, describes the summary vs full-schedule return difference, the capture_ref URI, and the alternate error payload. An agent has enough to invoke correctly and interpret the result.

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 every parameter including the nested envelope and defaults is already documented in the schema; the description largely restates the envelope semantics (summary/inline/capture) rather than adding new meaning. It does add the echoed debt_type/debt_type_label return fields, but those concern output, not parameter behavior. Baseline 3 is appropriate.

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 comparison task with a clear verb and resource: 'Compares the guaranteed return of debt payoff against expected investment returns over a time horizon' and 'finds the break-even investment return rate'. This is distinguishable from siblings like calculate_opportunity_cost or compare_strategies, and it enumerates supported debt types.

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?

Frames the decision question ('Should you pay extra on debt or invest the difference?') and gives explicit guidance on output mode selection (summary vs inline vs capture) and the transport restriction on capture. However, it never names a sibling tool as the alternative or states when NOT to use this tool, so routing is implied rather than explicit.

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