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

Annotations already cover safety (readOnly, idempotent, non-destructive, open-world), so the description's contribution is the behavior it adds: input units are milliseconds while the returned `t` is in seconds, plus the default window and the HIP-3 dex-prefixed coin convention. The unit asymmetry between input and output is exactly the kind of trap the annotations cannot express.

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?

Four tight sentences, front-loaded with purpose and return shape, then coin format, then interval, then time units. Every clause carries operational information; nothing is padding.

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?

With no output schema, the description carries the return-format burden and does so ('parallel arrays t/o/h/l/c/v', with `t` in seconds). Combined with defaults for interval and the time window, an agent has everything needed to call it correctly on the first attempt.

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; the description mostly restates the millisecond convention but does add the output-side note that returned `t` is seconds. It also narrows `coin` to 'BTC, not BTC-PERP', which sits slightly at odds with the schema's allowance for Discover perp ids like BTC-PERP — a minor inconsistency rather than a harmful one.

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 specific verb and resource ('Hyperliquid perp candles for one coin') plus the exact return shape as parallel arrays t/o/h/l/c/v, which immediately separates it from get_token_candles and the market-listing siblings. An agent can decide between perp and token candles from this sentence alone.

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 concrete operating context — interval defaults to 1h, the window defaults to the last 7 days, and the coin must be bare Hyperliquid form — but never states when to prefer this over get_token_candles or how it relates to list_perp_markets for discovering valid coins. Usage is implied by the 'perp' qualifier rather than spelled out.

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