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

The annotations already declare read-only, idempotent, closed-world, and non-destructive behavior. The description adds useful context beyond annotations: the data is monthly, refreshed at month-end, and sourced from Cyclesite's index series. It does not describe coverage limitations, but with annotations carrying the safety profile, a 4 is appropriate.

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 sentences front-load the scope, then give a concrete example and refresh cadence. There is no repetition or filler, and every sentence adds useful information.

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?

This is a simple two-parameter read-only tool, and the output schema exists, so return values need not be described. However, the description omits valid category values and default behavior when optional parameters are not supplied, leaving meaningful invocation gaps.

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 50%: months has a range in the schema, while category is undocumented. The description clarifies that months means a lookback and category means bike category (with a road-bike example), but it does not enumerate valid categories or state defaults when optional parameters are omitted.

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 states a specific resource (UK used-bike price trends), scope (last N months, by category), and source (Cyclesite index series). It is clear, but it does not explicitly differentiate from nearby siblings such as get_market_index or get_depreciation, so it falls short of a 5.

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?

An example question signals a typical use case, but there is no explicit when-not guidance or named alternative among siblings. The monthly-refresh note adds context but does not help the agent choose between this tool and related market tools.

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