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

Annotations only declare readOnlyHint=true, so the description carries the burden of describing the payload, and it does so concretely: memory count, last-updated timestamp, and the brain list with the in-use brain marked active. It does not mention cost, latency, or whether the status is computed live versus cached, which keeps it short of a 5.

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?

A single sentence that front-loads the purpose ('Health overview of the user's brain') and then lists the returned fields. No filler, no repetition of the title.

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 must convey return contents and it largely does, covering all three reported items. It stops short of describing the shape or units (e.g., timestamp format, whether counts are per-brain or global).

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?

The tool takes zero parameters, so the baseline is 4; there is nothing for the description to disambiguate beyond the fact that no scope or identifier is required.

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 names a specific resource (the user's brain) and enumerates exactly what is reported: memory count, last-updated time, and the account's brains with the active one marked. It is clearly a read/status tool, distinguishable from the mutation-oriented siblings (brain_memorize, brain_forget, brain_pin, brain_use), though it never names an alternative explicitly.

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?

Usage is only implied by the phrase 'health overview' – an agent can infer this is for inspection rather than recall or mutation, but there is no explicit when-to-use statement or condition that selects this tool over brain_recall or brain_verify.

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