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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's real contribution is "Free callers get 12-week delayed reference values" – a data-freshness caveat tied to account tier that no annotation conveys. It also discloses the returned change windows, though it says nothing about response shape beyond that.

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?

Two sentences, zero padding, and the core capability plus the 20-code scope are front-loaded ahead of the free-tier caveat. Every clause carries information.

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 usefully conveys what comes back (values plus multi-horizon changes) and the tier-based delay. It stops short of explaining currency behavior or error cases for invalid codes, but is sufficient to call the tool correctly.

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%, with codes documented and exemplified and the maxItems/minItems bounds present, so the baseline is 3. The description adds the useful enumeration of index layers (oil, gas, resins, pulp, board, films, finished packs), which broadens understanding of valid codes but does not document the currency parameter's behavior.

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 and resource with concrete scope: today's values for up to 20 PackIndex codes in one call, across any index layer, with 1w/1m/3m/1y change windows. This clearly separates it from siblings like get_index_history (historical) and single-index lookups such as get_live_index.

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?

"For watchlists and cost models" implies the intended use case but names no alternatives and gives no when-not condition. An agent can infer batch retrieval should be used over single-index calls, but this is left to inference rather than stated.

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