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

With no annotations, the description carries the behavioral burden. It does disclose source and granularity ('OKX daily candles', closing price only), which implies intraday quotes are unavailable via this tool, but it says nothing about failure modes such as unsupported symbols, dates before a listing, or missing candles, and nothing about auth or rate limits.

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, and the most important fact (what is returned, in what unit, for what date) is front-loaded. The secondary sentence adds the use case without diluting the core statement.

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 two-parameter read tool with full schema coverage and no output schema, the description covers what comes back (a USD closing price) and when to use it. It is thin on edge-case behavior (unknown symbol, date outside available history) and on whether there is a single scalar return or a richer payload, which is the remaining gap.

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%, so both parameters are already documented (date pattern AAAA-MM-DD UTC, symbol example BTC) and the baseline is 3. The description only adds that the price is denominated in US dollars and reaffirms the UTC convention, which is marginal 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 names the exact quantity returned (closing price), the unit (US dollars), the resource class (crypto asset), the temporal scope (a single date, UTC) and the data provenance (OKX daily candles). That fully qualifies the operation and separates it from siblings like get_market or get_asset, which are not pinned to a single historical date.

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?

'Useful to value a past buy or sale' gives an explicit, concrete use context for calling this tool. There is no stated exclusion or named alternative, so it stops short of a 5, but the agent knows the intended scenario.

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