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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), so the bar is lower. The description adds genuinely new behavioral context the annotations cannot express: the cost model ('Free: uses no credits') and the shape of the returned reference data. It does not discuss rate limits or freshness, keeping it out of the top band.

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 dense sentence plus a short cost note, with the highest-value information (what is returned) front-loaded and the action directive at the end. No filler and nothing repeated from the name or title.

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 no output schema, the description carries the burden of explaining the return payload and does so by listing the four categories of information returned. Combined with the cost note and the 'call this first' routing hint, an agent has everything needed to call and use 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?

The tool takes zero parameters, so the schema has nothing to document and the baseline of 4 applies. The description correctly adds no parameter noise and instead frames the tool as a formatting reference.

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 verb and resource ('List the marketplaces TicketsData supports') and then enumerates the exact payload: URL/ID formats, event-discovery and cross-market support flags, and valid mode values. That content signature clearly separates it from siblings like compare_marketplaces, find_events, and get_event_listings, which operate on live data rather than reference metadata.

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?

It gives an explicit trigger: 'Call this first when unsure how to format an input,' which tells the agent exactly when this tool should precede a data-fetching sibling. It stops short of naming when-not-to-use conditions or naming alternatives by name, so it falls just below the top band.

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