Set a Homey logic variable

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

Annotations already declare destructiveHint=true and readOnly=false, and the description adds valuable context: the type-matching constraint, the side effect on flows ('changing one can change what the house does next'), and the fact that it operates on existing variables only. This goes beyond the annotations and provides meaningful behavioral disclosure without contradiction.

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 description is concise and front-loaded. The first sentence states the primary purpose, followed by necessary context (type rules, side effects, and non-creation). Each sentence earns its place, with no redundant or filler content. It maintains a clear, efficient structure.

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?

For a simple tool with two parameters and no output schema, the description covers the essential aspects: the operation, type constraints, side effects, and the relationship to other tools. It could potentially mention error handling on type mismatch, but that is implied by the explicit type rule. Overall, it's adequately complete for the tool's complexity.

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%, so both parameters are documented. The description adds crucial semantic detail: the value must match the variable's existing type, and the variable must already exist. This clarifies the 'value' parameter beyond the schema's generic description and provides a constraint that affects usage.

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 clearly states the tool's action ('Writes a new value to an existing Homey logic variable'), specifies the resource (logic variable), and emphasizes the 'existing' constraint, which differentiates it from homey_variable_create. It also explicitly states it never creates a variable, providing clear distinction from sibling tools.

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 gives clear context on when to use this tool (to change an existing variable) and when not to use it (it never creates variables), and points users to homey_home_overview to discover existing variables. However, it does not explicitly name the alternative creation tool (e.g., homey_variable_create), so it's not fully explicit about alternatives.

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