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

No annotations are supplied, so the description carries the burden. It does disclose key modelling assumptions (3-year horizon, 27% corporate tax rate, R399/mo legacy baseline) which is useful behavioural context, but it never states that this is a pure computation with no side effects, nor how the numbers are returned. Adequate, but a mutation/side-effect disclaimer and return-shape note are missing.

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?

A single dense sentence that front-loads the verb and enumerates the four computed figures. It is efficient and free of filler, though the packed jargon (Section 8(1)(b), phantom fuel savings) makes it slightly heavy for one sentence.

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 no annotations, the description does the essential work of naming the four return values, so an agent knows what comes back. The only gap is that it does not describe the response structure (totals vs. per-vehicle) or confirm the computation is side-effect free.

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% and every property already documents its meaning and default (fleet_size default 3, sars_rate_per_km default 5.62, annual_business_km default 25000). The description adds no parameter-level detail beyond the schema, so the baseline 3 applies; it does at least anchor the vehicle bracket context indirectly through the tax framing.

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 opens with a specific verb ("Calculate") and then names the exact outputs: SARS Section 8(1)(b) deduction, 27% corporate tax cash return, phantom fuel savings, and 3-year contract savings. That is far more specific than any sibling (get_sars_summary, get_sars_compliance_guide) and an agent can tell this is a modelling/projection tool rather than a data-fetch tool.

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 only implied: the words "Calculate ... ROI" and "vs. legacy R399/mo tracking contracts" suggest a what-if / sales-projection scenario, but there is no explicit when-to-use or when-not-to-use statement, and no routing away from get_sars_summary or get_sars_compliance_guide. Nothing is misleading, but the agent has to infer the trigger condition.

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