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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description adds that results belong to a stateful 'current DERATE diagnosis' and enumerates the returned attributes, but says nothing about pagination, limits, or what happens when no diagnosis exists.

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 front-loaded sentence with no filler; the resource comes first and the returned fields are listed compactly at the end. Every clause earns its place.

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 usefully enumerates the returned attributes (severity, system, fault type, root cause) and the annotations carry the safety profile. It is nearly complete, lacking only behavior for the empty/no-diagnosis case.

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?

Only one optional parameter (lang) exists and schema description coverage is 100%, so the schema fully documents it including enum values and default. The description adds no extra meaning about the language parameter, so the baseline of 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?

Names a specific verb and resource ('List the fault codes (SPN/FMI)') and scopes it tightly to 'the current DERATE diagnosis', which implicitly separates it from siblings like search_fault_code_library or get_truck_fault_code. No sibling is named explicitly, so it stops short of a full 5.

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 through the phrase 'in the current DERATE diagnosis' — the agent can infer it applies when a derate diagnosis is active, but no when-to-use/when-not conditions or alternatives (e.g., searching the whole library) are stated.

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