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

With no annotations, the description carries the burden and does add real behavioral context: data can be up to 15 minutes stale, probabilities are rounded, the service is free, and prices derive from play-money Vpoints with no cash value. It still omits pagination/rate-limit behavior and roughly what fields or how many items come back.

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-loaded with what the tool returns, followed by cost and an interpretation note for the probability values. No filler; each sentence contributes distinct 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?

For a two-parameter listing tool with no output schema and no annotations, the description covers freshness and price semantics but leaves the default/limit behavior and the return shape unexplained. An agent can call it, but cannot predict result size or how 'most played' is measured.

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 only 50%: the category enum is documented in the schema, but 'limit' (1-50) has no description anywhere and is never mentioned in the description. The description adds no parameter meaning at all, so it fails to compensate for the coverage gap.

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-like action (retrieve most played open prediction markets) on a named resource (Vatic markets), with ranking ('most played') and status ('open') qualifiers. An agent can tell this is a discovery/listing tool, though it never names how it differs from siblings like live_markets or market_summary.

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 only implied: 'most played open' markets suggests browsing popular open markets rather than looking up a single market (get_market/live_market) or history. There is no explicit when-to-use statement, no exclusions, and no named alternative to route to when a different market view is needed.

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