Set System Variable

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

With only readOnlyHint=false available, the description carries the burden and does so well: it enumerates refusal paths (out-of-range, read-only variables, headless registry_sysvar, missing ezdxf header slot), the passthrough behavior for unknown variables, and the ValueError surface. This is well beyond what annotations convey.

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?

The core action is front-loaded in the first sentence, and the refusal semantics follow logically. The second and third sentences are dense with parentheticals but each clause carries distinct behavioral information, so little is wasted.

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 described, and annotations cover the write flag. Given that, the description supplies exactly the missing pieces: validation/refusal behavior, passthrough semantics, and engine-specific limitations that an agent needs to invoke this correctly.

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 100% for both parameters, so the schema already documents name and value. The description adds contextual meaning (that value is validated against a catalogue range/enum for known variables) but no syntax or format detail beyond that; baseline 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?

States a specific verb and resource ('Set an AutoCAD system variable') and immediately grounds it with concrete examples (DIMSCALE, LTSCALE, MEASUREMENT). It even hints at its sibling relationship by referencing system_variable_describe for range lookup, so an agent can place it precisely in the tool family.

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?

Explains the conditions under which writes are refused and directs the agent to system_variable_describe to check ranges, which is real usage guidance. It does not, however, contrast itself against nearby mutation tools like system_preferences_set or system_run_command, so the routing story is slightly incomplete.

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