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

Annotations already establish readOnlyHint/idempotent/non-destructive, so the safety profile is covered. The description adds genuine behavior beyond that: 'Deterministic arithmetic with the method explained,' plus the conditional nature of the month view (it only appears when sales_per_month is supplied) and the defaults applied for each scenario. It stops short of stating units or rounding of the returned figures.

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?

Purpose is front-loaded in the first sentence, followed by inputs and then the enumerated outputs. The output enumeration is long but justified because there is no output schema, so each clause earns its place; slightly denser than ideal but no filler sentences.

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 and nested objects across 7 parameters, the description is the only source of return-value information — and it enumerates margin/profit per creep level, the zero-profit overrun, the target-margin price, and the full month view including break-even sales and reserve coverage. Nothing an agent needs to call or interpret the tool 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 86%, so the parameters are largely self-documented and a baseline of 3 would hold. The description goes a step further by tying parameters to outcomes — sales_per_month enables the slow month view, cash_reserve drives the 'how many slow months the reserve covers' figure, and the creep/slow-drop defaults (10/25/50 and 40%) are surfaced in the narrative rather than left in the schema.

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?

Opens with a specific verb and resource: 'Show what scope creep and a slow month do to one fixed-price package.' It names the two stressors (creep, slow month) and the unit of analysis (one fixed-price package), which is enough to separate it from build_packages or compare_models without opening a 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?

The description gives clear situational context — use it when you want to see the effect of scope creep and a slow month on a fixed-price package — and lists the inputs that enable each view ('optionally sales per month and a cash reserve'). However, it never names or excludes the sibling tools (build_packages, compare_models, package_scope_language), so the agent has no explicit routing rule among them.

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