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

Annotations already declare readOnlyHint=true, so the agent knows this is a read. The description adds a genuinely extra behavioral fact not in the annotations: 'Free read' (no cost). It does not reconcile the odd idempotentHint=false / destructiveHint=true annotations, but it does not contradict the read-only nature either. Adding cost context to an annotation-covered read is worth a 3.

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?

Three short clauses, front-loaded with the core purpose, then the alternative, then cost. Every clause carries information with no filler. Slightly clipped rather than maximally clean, but tight and well-ordered.

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?

For a simple two-parameter read tool with no output schema, the description conveys what trajectory data means and when to prefer it. No output schema means return shape is unspecified, but the description conceptually covers the returned 'direction' of movement. Adequate for the tool's complexity.

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 both parameters (days, site_id) are fully documented in the schema. The description only restates the default window ('default 90 days'), adding no syntax or format detail beyond the schema. Baseline 3 is appropriate when the schema does the heavy lifting.

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 verb+resource ('Score trends over a window') and clarifies what the score means (SEO/AEO/GEO direction for a brand), so an agent knows exactly what data is returned. It references list_snapshots as an alternative, which aids differentiation, though the framing is cost-oriented rather than a clean purpose distinction.

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?

Explicitly names an alternative and the condition that selects this tool: 'Cheaper than list_snapshots when you only need the trajectory.' That is a clear when-to-use signal. It does not state when-NOT-to-use beyond the cost/trajectory tradeoff, so it stops short of a 5.

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