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

With no annotations, the description carries the full behavioral burden and does meaningful work: it states the auth requirement ("signed-in user or a bearer token"), the hosted-agent constraint, ownership semantics, and that the new brain is immediately readable/writable. It omits failure behavior such as what happens on a duplicate or over-length name, keeping it out of the top tier.

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 sentences, front-loaded with the resource definition before workflow and auth details, with no filler. The third sentence is slightly overloaded, stacking auth, hosted-agent behavior, and immediate usability into one clause.

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 single-parameter creation tool with no annotations and no output schema, the description covers concept, ownership, prerequisites, and the next step. It would be fully complete with a note on duplicate-name errors or whether the returned brain identifier is what brain_write expects.

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% and the schema itself already documents the 60-character limit, uniqueness, and examples for "name." The description adds the conceptual framing of what a Brain is but no additional syntax or constraint detail 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?

The description uses a specific verb ("Create") on a named resource ("Brain") and immediately defines that resource as "a named set of private Markdown memory" with concrete examples (project, client, store). This definitional work is what lets an agent distinguish brain_create from brain_get/brain_list/brain_search without opening any 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?

It gives clear usage context ("for a project, a client or a store") and routes the agent to the follow-up tool by name: "Then write files into it with brain_write." It stops short of explicit when-not guidance, but there is no competing creation sibling to exclude, so the practical gap is small.

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