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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds the meaningful behavioral fact that lookup accepts either a slug or a page URL and previews the payload shape, but says nothing about failure modes (invalid slug, off-site URL) that an agent would want when a lookup misses.

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 front-loaded sentence: the lookup key comes first, then the returned fields. The field enumeration runs long and the trailing Polish gloss largely duplicates the title, but there is no filler or hedging.

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 an output schema present, the description need not explain return values, yet it still previews them; annotations cover safety and idempotency. The only real gap is what happens on a bad slug/URL, which for a read-only single-record fetch is a minor omission.

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 value the schema does not: 'by its id (slug) or page URL' conveys that the two parameters are alternatives rather than cumulative, which the flat, all-optional schema does not express (only the example hints at the domain).

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 and resource ('One event on GdzieZabawa.pl by its id (slug) or page URL') and enumerates the returned fields, so an agent can tell this is a single-record lookup rather than a search. It does not name the sibling search_events as the thing it is *not*, so differentiation is implied by 'one event' rather than stated.

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?

Usage is implied: fetch details for a known event id or URL. The schema notes the id comes 'from search_events', but the description itself gives no explicit when-to-use/when-not or prerequisite (e.g. 'use search_events first to obtain an id'). Adequate but leaves routing to inference.

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