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

Annotations already declare readOnlyHint/idempotentHint/destructiveHint=false, so the safety profile is covered. The description adds real value beyond them: a tracking precondition, a plan gate ('Requires an Indie plan (trial counts)'), and result ordering ('newest first').

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-loads the resource and payload, then prerequisites, in efficient prose with no filler. Four short sentences, each carrying information, though the ordering/plan sentences could be tightened slightly.

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 carries the burden of explaining the return value and does so ('which apps ranked in the top results on each measured day, newest first'). Prerequisites and plan gating are covered; only pagination/volume limits are unaddressed, which is minor.

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 both parameters are already documented, making 3 the baseline. The description reinforces that the keyword must be tracked in the workspace, but adds no syntax or format detail the schema lacks, and says nothing specific about the days window.

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 verb and resource ('SERP history for one tracked keyword') and clarifies the payload: which apps ranked in the top results on each measured day, newest first. It is distinguishable from the per-app sibling sonar_app_rankings only by implication ('one tracked keyword'), so it stops short of explicit sibling differentiation.

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 a clear use case ('see who competes on a keyword and how the top spots shifted over time') plus prerequisites: the keyword must be tracked in the caller's workspace and an Indie plan is required. It names no explicit alternative tool (e.g. sonar_app_rankings for a per-app view), so it lacks when-not guidance.

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