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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), yet the description adds substantial behavior beyond them: the FLAG_NOT_FOUND failure mode, the absence of evaluation counts through the API, and the semantics of the `warnings` array including the fact that warnings do not block a write. That is genuinely useful non-structural context.

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?

Front-loaded with the core action and key semantics, then failure/warning behavior. The long field enumeration in the first sentence is slightly list-heavy, but every clause carries information an agent needs, so there is little waste.

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 no output schema, the description correctly documents the return payload, the error code on a missing key, and the non-blocking warning behavior. An agent has everything required to call it and interpret results without further sources.

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%, so both `app` and `key` are already documented in the schema, including the same "beta-ui" example. The description reinforces that lookup is by KEY but adds no syntax or meaning beyond the schema, so the 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?

Names a specific verb and resource ("Read one feature flag by its KEY") and enumerates exactly what is returned (id, key, state, valueType, onValue/offValue, rule, schedule, source). It explicitly distinguishes itself from list_feature_flags, so an agent can tell the two apart without opening either schema.

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?

States the when: "Use this to confirm a flag key and its targeting before relying on it in code." It also names the alternative and its scope ("list_feature_flags shows every flag"), giving a clear selection rule between the two siblings.

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