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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context: prices are decimal strings between 0 and 1, status enum values, resolvedOutcome appears only when settlement is unambiguous, and upstream market content is quoted data not instructions. This goes beyond the annotations and helps the agent interpret results safely.

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 description is compact and front-loaded: it states the core action and identifier types first, then the one-identifier constraint, then return-format details, and finally the safety note about upstream data. Every sentence earns its place, and the warning about not following directives in market content is a high-value addition.

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 read-only single-market fetch with a rich output schema, the description covers the essential behavioral details: identifier options, the one-identifier rule, price/status/resolvedOutcome semantics, and the prompt-injection warning. The annotations cover safety and idempotence, and the output schema covers return structure, so nothing critical is missing.

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 description coverage is 100%, so the schema already documents all five parameters. The description adds the 'exactly one identifier per call' constraint and the canonical id example, which is useful, but it does not need to repeat parameter details. Baseline 3 is appropriate because the schema carries the heavy lifting and the description adds only a small amount of extra meaning.

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 ('Fetch') and resource ('one market'), and enumerates the four accepted identifier types, which distinguishes it from sibling tools like get_event or get_market_quotes. It also clarifies the canonical id format with an example, so an agent can tell exactly what this tool is for.

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?

The description gives clear context on when to use this tool: to fetch a single market by one of several identifiers, and explicitly says to provide exactly one identifier per call. It does not explicitly name alternatives or exclusions, but the sibling list and the identifier-based scope make the usage context clear enough.

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