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

Annotations already cover the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false). The description adds value the annotations don't: an authorization rule ('Any org member except a Guest may add one') and default behaviors for unit/startValue. It omits the idempotencyKey retry behavior that the schema describes, which is the one notable behavioral gap.

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 dense sentences: purpose, parameter contract, authorization. Required parameters and the one branching parameter are front-loaded; no sentence is padding.

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 7-parameter mutation tool with no output schema, it covers the required inputs, defaults, enum usage, permissions, and the manual-vs-rollup fork. The only meaningful omission is any mention of the idempotencyKey retry contract, which the schema handles but the description ignores.

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 the baseline is 3. The description goes beyond the schema by restating required vs. optional grouping, the >0 constraint on targetValue, defaults for unit/startValue, and the enum values plus the semantic meaning of omitting rollupMethod (manual updates).

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?

Specific verb+resource+parent: 'Attach a measurable Key Result to an existing goal.' An agent can immediately separate this from create_goal (creates the parent) and update_key_result_value (mutates an existing KR).

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?

It routes one decision explicitly: leave rollupMethod unset for manual updates via `update_key_result_value`, which names the sibling tool and the condition that selects it. It also states who may call it. It does not give broader when-to-use context vs. create_goal, but the create-vs-update boundary is implied clearly by 'existing goal'.

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