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

Annotations already declare readOnly/idempotent/openWorld, so the description adds the genuinely non-obvious behavior: three distinguishable response states and the explicit guarantee that a nonexistent slug returns error 'not_found' with settled: null rather than 'still open'. It also discloses a real limitation — no settlement timestamp is available on this endpoint.

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 the core answer, then the outcome taxonomy, then usage. The three-outcome enumeration is long but each branch carries distinct agent-relevant meaning; only the parenthetical 50/50 explanation is mildly redundant.

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 return-value burden and does so precisely: it names the fields (settled, price, error), the values for each state, and what is absent. An agent can call this correctly and interpret every response without further documentation.

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 the single slug parameter is already documented as coming from polymarket_us_search. The description reinforces the slug-based lookup but adds no format, casing, or example semantics beyond what the schema provides, so the baseline applies.

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 ('Settlement (resolution) result for one Polymarket US market by slug') and immediately defines the value semantics (1 winner / 0 loser / fractional for partial). This cleanly separates it from siblings like polymarket_us_search, polymarket_us_bbo, and polymarket_us_price_history.

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 after polymarket_us_search / a known slug to check how a market actually resolved' gives a clear trigger and prerequisite. It does not explicitly name a when-not or an alternative tool to prefer (e.g. resolution_audit / resolution_diff), so it stops short of full routing guidance.

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