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

With no annotations, the description carries the full burden of behavioral disclosure and does well: it states 'Pure static data, always returns 200, no authentication required, sub-50ms p95,' plus model-agnostic and compliance attributes. However, it claims to return 'market hours metadata' and 'exchange operating hours metadata,' yet the specified return schema only includes mic, name, timezone, and mic_type—no actual operating hours. This is a minor misrepresentation that prevents a perfect score.

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 well-structured and front-loaded with purpose and when-to-use guidance. However, it is verbose, listing all 28 exchanges with full names and codes, which is redundant given the tool returns that same data. Most sentences serve a purpose, but the exhaustive enumeration could be condensed without losing essential guidance.

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?

Given no output schema, the description compensates by explicitly providing the return shape ({ exchanges: Array<{ mic, name, timezone, mic_type }> }) and operational constraints. It also gives a complete market coverage breakdown and performance expectations. The main gap is the inconsistency between the promised 'market hours metadata' and the actual returned fields, which could mislead an agent expecting schedule information.

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 has 0 parameters, so the baseline is 4. The description appropriately doesn't discuss inputs, as there are none. It correctly focuses on output and usage context, adding no misleading parameter information.

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 opens with 'Returns directory of all 28 exchanges supported by Headless Oracle: MIC codes, exchange names, IANA timezones, market hours metadata, and mic_type (iso|convention).' This clearly states the verb (returns), the resource (directory of exchanges), and the exact fields. It also distinguishes itself from siblings by explicitly framing itself as the discovery surface to use before get_market_status or get_market_schedule, so its unique role is obvious.

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 contains a dedicated 'WHEN TO USE' section: 'call once at agent startup to discover supported markets before calling get_market_status or get_market_schedule.' It names the alternative tools and provides concrete context for when this tool is the right choice, and hints at exclusions (not for status/schedule queries).

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