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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is established. The description adds useful behavior context: it clarifies that the data is a managed internal reference series, that aggregates are fixed 24h, and that no authentication is needed. This goes beyond the annotations without contradicting them.

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 two sentences, packs in the purpose, key details, and limitations, and is front-loaded with the action. No wasted words.

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 simple read-only price series tool with a single optional parameter and an output schema, the description covers the essential context: what it returns, its limitations, and auth requirements. It is complete enough for an agent to select and invoke 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?

The schema already provides 100% coverage for the single optional parameter, including the range and the fact that 24h aggregates are unaffected by the lookback window. The tool description doesn't add new parameter-specific meaning; it merely reinforces what the schema states. 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?

The description clearly identifies a read operation ('Read') targeting a specific resource (DB-CPTM reference rate series) and lists the data elements (high/low/change/volume). It also distinguishes the tool from potential siblings by noting it's a 'closed-economy reference figure only,' which sets it apart from transactional or external settlement tools.

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 provides clear context for when to use this tool: to access internal CPTM reference rates. It also states exclusions ('no external redemption, withdrawal, or chain settlement') and notes that no auth is required. However, it does not explicitly name alternative tools, so it stops short of full guidance.

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