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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false, and destructiveHint=false, so the safety profile is covered. The description adds substantial behavioral context beyond that: it discloses the return payload structure (rule + version + sha256 hash of canonical JSON), explains the settleable flag and its conditions (source's terms allow it and grade is not display), and even maps the response to a REST endpoint — all of which help an agent reason about downstream use without contradicting the annotations.

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 a single dense, front-loaded sentence that leads with the usage trigger, which is good structure. However, it packs a long enumeration of rule fields plus a settleable explanation into one unwieldy sentence, which reduces scannability and makes it harder to isolate the key call conditions — efficient in word count but not in information architecture.

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 burden of explaining return values, and it does so thoroughly by enumerating the rule components, version, hash, and the settleable flag with its conditions. The main gap is that it does not mention error or not-found behavior for an invalid ticker, so it is not fully complete for a tool an agent may call speculatively.

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 describes the single ticker parameter including the 'with or without the dollar sign' detail, so the schema already does the heavy lifting. The description does not add parameter-level syntax or format guidance beyond what the schema provides, so a baseline 3 is appropriate.

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+resource (retrieve the machine-readable rule for a Tickerz index) and enumerates exactly what the rule contains — source, query, transform, aggregation, cadence, unit, decimals, precision, revision policy, grade, settlement rights with terms page and quoted clause, version, and hash. This is precise enough to distinguish it from siblings like get_index or methodology without opening their schemas.

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?

Opens with an explicit when-to-use condition — 'Use when someone needs to know exactly how a Tickerz index is counted before relying on it' — which is a clear contextual trigger. However, it does not name alternatives (e.g., methodology, get_index) or state when NOT to use this tool, so the routing guidance is incomplete.

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