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

Annotations already declare readOnly/idempotent/non-destructive/openWorld=false, so safety is covered. The description still adds real behavioral value: result cap of 20, the `next_cursor` pagination mechanism, city-local time semantics, and the note that organizer-authored titles/descriptions arrive as plain data (a useful prompt-injection caveat).

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 purpose, then usage, then return shape — a sensible order. It is slightly padded: the long genre list partially duplicates the `categories` enum and the prose is denser than needed, but no sentence is wasted.

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 a 15-parameter tool with a nested `near` object, the description covers purpose, when to use, result count, pagination and time semantics; an output schema exists so return values need not be detailed. It stops short of covering city-vs-near mutual exclusion, which the schema handles.

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% and every parameter is documented in-schema with enums, defaults and ranges, so the baseline is 3. The description maps a few user intents to parameters (free events, near a place, genre/performer) but adds little syntax or default detail beyond what the schema already carries.

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 concrete verb and resource ('Search the СПОНТАННО events listing') and scopes the domain (concerts, theatre, standup, etc., in Russian cities). It explicitly contrasts itself with the sibling spontanno_random_event ('A single surprise pick is what spontanno_random_event is for'), so an agent can route without opening either 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?

'Use this when the user wants options' enumerates the triggering intents — what's on today/tomorrow/weekend, genre, performer, venue, free events, near a place — and names the alternative tool for the single-pick case. Both when-to-use and the exclusion are present.

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