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

Annotations already declare readOnlyHint=false and destructiveHint=true, so the agent knows this is a mutation. The description adds valuable behavioral context beyond annotations: it specifies the owner token requirement, a reserved key name, and a failure mode for old publications (409 OLD_PUBLICATION_READ_ONLY with createUrl). This is substantial added value, though it doesn't cover success response behavior.

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 four sentences, front-loaded with the core purpose, followed by prerequisites, a reservation, and an error case. Every sentence serves a purpose, though the error detail could be slightly condensed. It is well-structured and avoids fluff.

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?

Given a destructive mutation tool with full schema coverage and no output schema, the description covers key behavioral aspects: authentication requirement, reserved key, and a specific failure mode. It does not describe the return value on success, which is a minor gap since no output schema exists. Overall it provides enough context for an agent to invoke the tool correctly.

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 the schema already documents all five parameters. The description adds only a specific constraint on the `key` parameter (the value `hosting` is reserved), but does not explain the meaning or format of namespace, id, value, or ownerToken beyond what the schema provides. Baseline 3 is appropriate when schema does the heavy lifting.

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 verb and resource: 'Set or update a key in an existing BrewPage KV store.' This clearly distinguishes it from read operations like get_kv and implies it works on an existing store (unlike publish_kv, which may create one). However, it does not explicitly name sibling tools or contrast its purpose with them, so it falls short of a 5.

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 prerequisites (requires owner token) and a restriction (key name `hosting` is reserved), but it does not say when to use this tool versus alternatives such as get_kv or publish_kv. Usage is implied by the verb 'set or update', but there is no explicit guidance on when-not-to-use or which sibling to choose in different scenarios.

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