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

Annotations already cover the read-only, non-destructive, closed-world profile, and the description adds genuinely new behavior: null means 'checked and not in the top-10', results are never interpolated, and an empty result can have a configuration cause rather than a data cause. It stops short of saying whether the series is ordered or bounded, but the disclosure is well above the annotation floor.

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 purpose, then layered with return semantics, empty-state cause, and prerequisite in a logical order; every sentence carries information. It is on the dense side (parenthetical null definition, inline config explanation) but not padded.

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 takes on the return-value burden and does so by naming the three things returned per keyword plus the null convention. The only gap is structural detail — actual field names and whether the check series is ordered or limited — which an agent may need to parse the response.

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 are already described in the schema, and the description adds nothing parameter-specific — its detail is entirely about return semantics. Baseline 3 is appropriate when the schema carries the parameter burden.

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?

Opens with a specific verb+resource ('Rank history for a product's tracked keywords') and immediately scopes it to scanner scan passes, which separates it from sibling tools like get_scan_history or get_keyword_ideas. The per-keyword return contents (latest, best, series) further pin down what the tool actually yields.

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 states the two preconditions an agent must check — a plan with the keyword_research facility and a configured SERP source (searchConfigured=false → empty board) — which is real usage guidance. However, it never says when to prefer this over run_keyword_research or get_scan_history, nor what to do when the board is empty (configure vs. wait).

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