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

With no annotations, the description carries the full burden. It discloses the authentication requirement and enumerates the complete return field list (brain, role, name, folder, size, context membership, sharing status, change time). The read-only nature is implied by 'List'. It omits potential pagination/limit behavior but covers the essentials.

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?

Two sentences, front-loaded with the primary action and scope, followed by the auth and response details. Every clause carries information; there is no filler or repetition of schema content.

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?

Although there is no output schema, the description explains what a Brain is, defines the list scope, states the auth requirement, and enumerates the returned fields. For a simple, zero-required-parameter listing tool, this is sufficient for correct invocation and interpretation of results.

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 both optional parameters (brain and folder) with format examples. The description adds no parameter-specific detail beyond the schema; the 'shared with you' mention echoes the schema's owner-handle/name format. Baseline 3 is appropriate.

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 and resource: 'List the files in your Brains', and further clarifies scope with 'including brains shared with you'. This clearly differentiates it from siblings like brain_get (single-item retrieval), brain_search (query), and brain_write (mutation) without needing to open schemas.

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 clear usage context (listing files in personal and shared brains) and a key prerequisite (bearer token). It doesn't explicitly name alternatives or exclusion conditions, but the purpose is specific enough that an agent can infer when to choose this over a search/get/write tool.

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