Describe System Variable

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

Annotations give only readOnlyHint=true; the description carries substantial extra context: unknown names are never an error (known:false plus nearest catalogue names), `current` is omitted with a `current_unavailable` reason when the backend cannot read it (no document open, registry variable headlessly), and engines.ezdxf:false signals a refused write. That is rich behavioral disclosure beyond the annotation.

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-loaded with the core purpose in the first line, then the three modes and edge cases. Dense but every clause earns its place; the parenthetical about friendly_key/engines is long but conveys non-obvious operational facts rather than filler.

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?

An output schema exists, so return values need not be explained, yet the description still enumerates the returned fields and their edge cases, and covers all three input modes plus failure behavior. Nothing an agent needs to call this correctly 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 already 100%, so the baseline is 3, but the description adds genuine semantics the schema lacks: `search` matches rows whose name OR meaning contains all the words, and `name` accepts a '$'-optional, case-insensitive form. This meaningfully enriches how the two parameters behave.

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 verb+resource: it describes what an AutoCAD system variable means, sourcing from 'an authored catalogue of 90'. The three operating modes are spelled out, so an agent can distinguish this lookup tool from system_get_variable and system_set_variable 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?

Explicitly routes between the three invocation shapes: `name` for a single variable, `search` for free-text over names/meanings, and neither for the index of names, plus a fallback for unknown names. It does not, however, contrast itself against the sibling system_get_variable, which is the one remaining piece of routing guidance an agent might want.

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