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

Beyond the annotations (which already cover read-only/idempotent safety), the description discloses real behavioral traits: no provider call and no credit spend, the null-vs-not-found semantics of `position`, the legacy `searchedDepth: null` meaning, and same-day collapse to the latest reading. That is exactly the kind of interpretation guidance annotations cannot carry.

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 identity, then cost, then edge-case semantics — a sound ordering with no obvious filler. The illustrative clause 'the same series the app's SERP-history chart draws' is pleasant but slightly padded given the rest of the sentence already says it.

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 must carry the return-value burden, and it does: ordering (oldest first), granularity (one point per UTC day, latest same-day reading wins), and the two null cases. Combined with annotations covering safety and schema covering inputs, an agent has everything needed to call and interpret this tool.

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% and each parameter already carries its own guidance (including the sinceDays range and default), so the baseline is 3. The description's null/ordering notes concern returned values rather than the input parameters, so it adds nothing further on that dimension.

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 and resource ('per-keyword position series over time, oldest first') and pins the scope to 'one tracked keyword,' which separates it from the config-level trend siblings like get_rank_config_trend. An agent knows exactly what it retrieves without opening the 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?

The 'FREE: database only. No SEO data provider is called and no credits are spent' line gives a concrete cost signal that shapes tool choice among the many rank-related siblings. However, it never names an explicit alternative or states when this tool is the wrong choice (e.g. a config-wide view).

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