Write L-Var

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

Annotations already signal mutation, idempotence, and open-world effects. The description adds substantial behavior beyond that: it reveals the native SimConnect mechanism, the compatibility with Fenix aircraft, and the crucial verification semantics ('verified': true/false/null with 'false or null is never reported as success'). This is exactly the kind of non-obvious behavioral context an agent needs when deciding whether to trust the result of a write.

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?

Three tight paragraphs, each carrying a distinct purpose: the core action, the implementation/compatibility detail, and the verification semantics. There is no filler or repetition. The primary purpose is front-loaded, and every sentence 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 an output schema present, the description does not need to enumerate return fields beyond the critical 'verified' semantics it already explains. Two required parameters are fully documented in the schema, and the description covers the operational context (current aircraft, Fenix compatibility, no MobiFlight). Nothing an agent needs to call this tool 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 description coverage is 100%; both parameters ('name' and 'value') already have clear descriptions in the input schema. The tool description restates the operation but adds no new meaning about the parameters themselves, so baseline 3 is appropriate.

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 states a specific action ('Write'), resource ('L-var'), and scope ('on the current aircraft'), and it further distinguishes itself by explicitly noting it does not use MobiFlight RPN, separating it from sibling tools like msfs_execute_calculator_code. The L-var vs simvar distinction is carried by the name and reinforced by the description. This is a clear, unambiguous purpose.

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 provides concrete usage context: it works with proprietary aircraft like the Fenix A320/A321 and does NOT require MobiFlight. This implies when to prefer this tool over MobiFlight-based approaches. It does not explicitly name alternatives such as msfs_set_simvar or state exclusions, but the 'does NOT require MobiFlight' clause gives sufficient selection guidance for an agent comparing siblings.

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