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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint, so safety is covered. The description adds behavioral context by specifying the returned data structure (market_data, community_data, etc.) and the date format requirement, which goes beyond the schema. However, it doesn't discuss error handling or rate limits, but that's acceptable given the simplicity.

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, no filler. The first sentence defines the tool and its key constraint (date format), the second gives usage direction and alternatives. Well-structured and front-loaded.

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 the output schema exists, the description need not detail return fields exhaustively, but it still lists the main categories. It covers the required parameter, format, and usage distinction. It is complete for a read-only snapshot tool, leaving nothing essential for an agent to call it 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 coverage is 67% (id and date have descriptions). The description reinforces the date format (dd-mm-yyyy) and that date is required, but this is redundant with the schema. It adds no new information about localization (which has a default). Thus it provides minimal additional value over the schema.

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 states it provides a snapshot of one coin on a single calendar day, with a specific date format. It distinguishes itself from sibling tools by naming the continuous series alternatives, making its purpose unambiguous.

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?

It explicitly instructs when to use this tool ('Use it for one fixed point in time') and directs to market_chart or market_chart_range for continuous data. This provides clear selection criteria among siblings.

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