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

readOnlyHint already declares a safe read, so the description earns credit for the added cost disclosure ($0.05 per call) and clarifying the computation basis. However it says nothing about what the response contains (per-coin premium/discount fields, handling of missing coins, reference-rate timing) beyond that annotation.

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 tight sentences with the cost and the core computation front-loaded; little waste. The trailing tagline 'arbitrage signal no single ticker shows' is slightly promotional but does convey differentiation.

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 single-param read-only tool with no output schema, the description explains what is computed and what it costs, which is enough to call it correctly. Missing only return-shape detail, which is minor here.

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% with one param ('symbols', comma-separated, up to 8), so the schema already carries the parameter meaning. The description adds no syntax or format detail beyond it, so baseline 3 is appropriate.

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 a specific computed resource (Indodax IDR price vs global USD spot converted at USD/IDR reference, premium/discount in percent), which is more than a restatement of the name. It implies differentiation from a plain ticker ('no single ticker shows') but does not explicitly name the sibling indonesia_crypto_idr.

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?

'The arbitrage signal' frames implied usage, but the description never states when to pick this over indonesia_crypto_idr or indonesia_fx, nor any exclusions or prerequisites. Usage is implied rather than prescribed.

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