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

Goes well beyond the annotations: it discloses that the folder is SUBSCRIBED and therefore visible in subscribed-only clients, that '/' builds hierarchy and auto-creates missing parents, that matching against existing folders is case-insensitive and returns the existing folder, and that it REFUSES names with blank segments. These are exactly the mutation/side-effect details annotations cannot convey.

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-loads the core purpose and each clause carries distinct information (subscription, hierarchy, idempotency, refusal). It is long and leans on shouty all-caps emphasis ('SUBSCRIBED', 'IN THE NAME BUILDS A HIERARCHY', 'REFUSES'), which costs some readability, but little is genuinely redundant.

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 still covers the return signal ('the reply says whether it actually created anything'), the mutation/idempotency behavior, and the error condition (blank segments). Everything an agent needs to call this correctly is present.

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 already 100%, so baseline is 3, but the description adds real semantics: '/' nests rather than appearing literally, a literal '/' is therefore illegal in a name, and `parent` may legitimately be a non-selectable folder because nesting under it makes it selectable. That is meaningful behavior beyond the schema strings.

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+resource ('Create an IMAP folder') and immediately differentiates from siblings like rename_folder/delete_folder by describing hierarchy-building and subscription outcomes rather than just restating the title. An agent can identify the operation without opening the 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?

Gives clear context on when this is the right call (asserting the folder lands where expected, is subscribed, and nests via '/'), and notes the idempotent existing-folder case so the agent knows re-calling is safe. It never explicitly routes to an alternative (e.g. rename_folder) or states when NOT to use it, so it falls short of the 5 bar.

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