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

Annotations already declare this is a non-idempotent, non-destructive write, so safety is covered. The description adds useful domain constraint context by stating key results must be quantifiable and require initial, target and direction values, but it says nothing about return format, ownership/permission needs, or validation failures beyond the schema's ownerId note.

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?

Two short sentences, well front-loaded with the primary action followed by the quantifiability requirement. No filler, though the second sentence could be tightened or expanded into more concrete field guidance.

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 9-parameter mutation tool with no output schema and very low schema description coverage, the description is thin: it omits what the created result looks like, defaults for unit/weight, and the enum meanings. Annotations cover the safety profile, but the parameter surface remains largely unexplained.

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 only 11% across 9 parameters, so the description must carry weight. It does clarify three parameters in domain terms (initial value, target value, direction of travel), but leaves unit, weight, title, objectiveId and description entirely to the raw schema, so it only partially compensates.

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 ('Add a measurable key result to an existing objective'), which clearly separates it from create_objective and the update_key_result family. It stops short of naming those siblings, so the agent must infer the boundary itself.

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?

'to an existing objective' implies the precondition that the parent objective must already exist, giving some implied usage context. However, there is no explicit guidance on when to choose this over create_objective or update_key_result_value, and no stated exclusions.

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