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

With no annotations, the description carries the burden, and 'Fetch' plus the field listing establishes a read-only detail lookup. It discloses the returned data shape, which matters since there is no output schema. It does not mention what happens for an unknown slug, null fields, or caching, so a 4 rather than a 5.

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?

One sentence, front-loaded with the verb and the identifying parameter, then the return payload. No filler or redundancy.

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?

The tool is low-complexity with only two parameters, and since no output schema exists, the description usefully enumerates the returned fields including the twelve monthly season factors. Combined with schema coverage of both parameters, an agent has everything needed to call it correctly.

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 the baseline is 3, but the description adds real meaning by tying the required 'slug' parameter to its source (list_cities), which the schema does not. It says nothing about the optional 'lang' parameter, but the schema documents that fully.

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 ('Fetch one city by its slug') and immediately enumerates the returned attributes, so the agent knows exactly what it gets. The parenthetical '(from list_cities)' explicitly separates it from the list_cities sibling, which returns many cities.

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 '(from list_cities)' note establishes the workflow: use list_cities to discover slugs, then call this for detail on a single city. It never states an explicit exclusion or error condition (e.g., behavior for an unknown slug), so it falls short of a full when/when-not statement.

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