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

Annotations already declare read-only, idempotent, open-world, non-destructive, so the safety profile is covered. The description adds genuine context beyond that: the exact return fields (name, legal operator, country, city, website, registry status), the operating/segment distinction, and the presence of segment_count on operating MICs. It doesn't say what happens on an invalid or unrecognized code, which keeps it from a 5.

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 decode action and the resource definition, then the operating/segment distinction and the sibling hand-off. The first sentence is long and stacks two parentheticals, but every clause carries information an agent needs.

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 correctly spells out the returned fields and the operating-vs-segment shape, which is exactly what's needed for a single-parameter lookup. It omits error behavior for a malformed or unknown MIC, the one gap.

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% so the parameter is already documented, but the description adds meaning: the code is the same identifier openfigi exposes as exchCode and the form market-data feeds use, which helps the agent map it from other data. Examples in the schema reinforce rather than replace this.

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 (decode) and resource (ISO 10383 MIC), and defines the resource in terms an agent can recognize ('the 4-character venue code openfigi returns as exchCode'). It further distinguishes the two output categories, OPERATING vs SEGMENT MIC, with concrete examples (XNYS, ARCX), which no sibling does.

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?

Explicitly routes the agent: 'call search_mics with operating_mic to list them' when segments are needed, giving a concrete alternative and the condition that selects it. It doesn't cover the reverse case (use search_mics when the exact code is unknown), so it stops short of full when/when-not coverage.

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