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

Annotations already cover read-only/idempotent/closed-world, but the description adds genuinely new operational facts: it is FREE, database-only, issues no new SERP calls, spends no credits, and is derived entirely from stored history. That cost/data-source disclosure materially affects whether an agent should call it.

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-loaded with the core definition and the free/no-calls constraint, and most sentences earn their place. The 'Modeled on AccuRanker Grump Rating' and 'MozCast calibrated against hundreds of thousands of keywords' passages are somewhat tangential for selection purposes.

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 usefully explains what volatilityIndex means and how to interpret it (relative, CTR-weighted, not absolute severity). Complete enough for a 4-param read tool, though return shape/series granularity is left implicit.

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%, so every parameter including the no-op device enum, runLimit range, and configId pointer is already documented in the schema. The description adds no parameter-level detail beyond what the schema provides, making 3 the correct baseline.

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 resource ('SERP volatility index') and precisely defines the measure as this tracker's own run-over-run churn. It explicitly distinguishes itself from the Sensor score, MozCast, and mood labels, so an agent can tell what it is and is not without opening a 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 strong interpretive guidance ('meaningful only relative to THIS tracker's history', don't call a value high/low in isolation) but never routes the agent among siblings — no mention of when to prefer get_rank_movers, get_rank_config_trend, or get_rank_keyword_history. Usage context is implied, not enumerated.

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