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

With no annotations, the description carries the full burden and does well: it discloses the point-in-time guarantee (nothing under `then` leaks from later), labels which figures are forward-looking, and notes the cost ('one call costs one answer'). It does not describe error behavior for out-of-range `at` values or response structure beyond field names, leaving a modest gap for a read tool with zero annotation coverage.

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 capability, then the sibling routing, then the point-in-time semantics, then the parameter constraint — a sensible order. The middle sentence stacks many clauses and is slightly dense, but no sentence is filler.

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?

There is no output schema, so the description enumerates the returned measures itself, and it covers timing semantics, sibling selection, and the constraint on `at`. For a two-parameter read tool, an agent has everything needed to call it correctly and interpret the result.

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 baseline is 3, but the description adds real meaning beyond the schema: `at` must be a UTC ISO-8601 moment inside the asset's range, and that range is discoverable via list_coverage. It also implicitly frames `asset` as selecting the market being read. The syntax itself (exact ISO format) is still only in 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?

States a concrete verb and resource ('Read what the market was at one moment') and immediately enumerates the measures returned: 1h/24h/7d/30d returns, day high/low/volume, volatility vs its own month, drawdown from week's high. It explicitly differentiates from the sibling get_price_paths, so an agent can pick between them without opening either schema.

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?

Gives an explicit selection rule: use this for one moment's numbers, use get_price_paths for the price path around a moment or several moments at once. It also routes the agent to list_coverage to discover the valid time range for an asset. Both when-to-use and the alternative are named.

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