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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds genuinely new behavior: results are reported over a window and against the previous equivalent window, which the agent would not know from annotations or schema. It does not state response shape or how the comparison is expressed, which slightly limits 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?

Two sentences, both load-bearing: the first front-loads the capability and the per-link vs split-by-dimension dichotomy, the second routes site-traffic queries elsewhere. No filler, and the enumeration of dimensions mirrors the enum without wasting words.

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 an 8-parameter, read-only analytics query, the description covers scope, comparison behavior, and the link_id/by interaction, with the schema handling formats, defaults and bounds. The notable gap is the return shape: with no output schema, the agent cannot tell how the previous-window comparison is represented in 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 description coverage is 100%, so baseline is 3. The description goes beyond it by explaining the interaction between link_id and by — omit link_id for all links, supply it to split one link by referrer/country/device/etc. — which the per-property schema text does not make explicit.

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?

Names a specific verb+resource (clicks and visitors on short links) plus the two output shapes: per-link rows, or a single link split by a chosen dimension. It also explicitly disclaims site-traffic reporting and points to get_overview/get_breakdown, so an agent can separate this from its closest siblings 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 clear routing context: use this for link clicks, not for site traffic, which lives in get_overview and get_breakdown. It also implies the by/link_id combination for drilldowns. It stops short of naming alternatives like get_timeseries or criteria for choosing among the remaining click-related views, so no explicit when-not beyond the site-traffic exclusion.

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