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

Annotations declare readOnly/idempotent/non-destructive, and the description adds critical response-shape behavior beyond them: bare array, positional rows, timestamps in milliseconds, no field names, no volume, and candle width derived from days. This anticipates common parsing mistakes and sets accurate expectations.

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?

Three sentences with no fluff: it front-loads the unusual response format, then the key derivation rule, then the alternative tool. Every sentence adds unique value and the length is appropriate for the tool's complexity.

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 a read-only, idempotent tool with an output schema and fully documented parameters, the description covers the non-obvious response format, the required days parameter role, and the main sibling alternative. Nothing critical is missing 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 has 100% parameter description coverage, so the baseline is 3. The description adds the semantic insight that candle width is derived from the `days` parameter, which is useful context not present in the schema, justifying a slight bump. It does not redundantly restate parameter names or formats.

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 states a specific output: OHLC candlestick data for one coin in a bare positional array, with explicit mention of timestamp, open, high, low, close. It distinguishes itself from the sibling market_chart tool by noting what it does not provide (volume) and what it is used for. No ambiguity about what resource and verb are involved.

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 says when to use this tool ('for candle or technical analysis') and names the exact alternative tool to use when price line plus market cap and traded volume are needed. This is direct routing guidance with a named sibling, leaving little to inference.

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