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 mutates state. The description adds genuine side-effect detail beyond that: it stores the measured size for the brain and starts the session's time box. It does not explain what makes the operation destructive or what prior state may be overwritten, leaving a notable gap against the destructive hint.

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 with no filler; the input contract is stated first and the return plus side effects follow. Nothing is redundant, though the phrasing is dense with project jargon ('first build', 'brain', 'time box') that adds no clarity.

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?

There is no output schema, so the description carries the return burden and does give a rough shape ('time-boxed plan with the coverage each tier reaches'), plus the write side effects. It stops short of describing the plan's structure or the relationship between tiers and coverage, which an agent would need to set expectations for the caller.

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 tier, brain, and the nested source fields are already fully documented in the schema, including the enum values and the 'about 20/40/60 min' mapping. The description only restates 'item count per source' and 'low, mid, high' without adding format or edge-case guidance. Baseline 3 is correct.

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 operation: it takes per-source item counts plus a depth tier and returns a time-boxed plan with per-tier coverage. That is a concrete verb+resource, not a restatement of the name. It does not, however, differentiate itself from adjacent siblings such as scan_status, run_start, or activation_stage, which an agent must disambiguate on its own.

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?

'Size the first build' and 'starts the session's time box' imply this is the sizing/planning step that precedes a scan session, which is usable context. But the description never states when to call this versus scan_status or run_start, and offers no exclusions or prerequisites. Usage is implied rather than stated.

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