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

With no annotations, the description carries the full burden and largely meets it: it discloses the read-only nature (HTTP GET), the pricing/auth model ($0.02 via x402), the evergreen roll-forward behavior, and the extra response fields (current_slug, rolls_to_next_at). It stops short of describing refresh cadence or failure modes, but the behavioral disclosure is solid.

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?

The core content is front-loaded and the metadata bracket is a compact, useful footer. However, the central question is stated twice ('Who controls the Senate after the next election?' appears in both the opening and the second sentence), which is avoidable redundancy.

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 zero-parameter read tool with no output schema, the description is nearly sufficient: it identifies the market, the evergreen resolution behavior, and the response deltas (current_slug, rolls_to_next_at) relative to the standard probability shape. It does not spell out what that standard shape contains, but it reasonably defers to a documented shared format.

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 per the baseline there is nothing to document and the schema (100% coverage, empty) already handles it. The description correctly adds no redundant parameter prose.

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 names a specific resource and the exact question it answers ('Who controls the Senate after the next election?'), which is inherently distinct from its evergreen siblings such as house-control-next-election. It is clear and unambiguous, though it does not explicitly route the agent away from any sibling.

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 explains the evergreen value proposition ('Auto-resolves to the current market instance and rolls forward on resolution'), which implicitly tells the agent to use this for the recurring question rather than a fixed-slug lookup. However, it never explicitly names an alternative such as probability_get or states when NOT to use it.

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