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

The description adds substantial behavioral context beyond the readOnlyHint annotation: it is a paid call at a flat per-call price, enabling `updates` does not change the price, the reading is based on closed buckets, and unavailable exchanges produce an error that is not charged. This gives the agent clear expectations about side effects, cost, and failure semantics.

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?

The description is tightly written with no wasted words. It front-loads the core purpose and result, then follows with pricing, optional-parameter behavior, and error handling. Every sentence contributes useful information.

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 tool with one optional parameter, a readOnly annotation, and no output schema, the description is complete: it covers what the tool returns, how to modify the call, cost implications, and error behavior. An agent has enough context to select and invoke 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?

The schema already documents the single `updates` boolean with a description, so baseline is 3. The description adds extra meaning by clarifying what the updates flag appends (rolling intra-day reading from the last closed sub-daily bucket) and that pricing is identical either way, adding value beyond 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 states a specific verb ('Get'), a specific resource ('Bitfinex cross-exchange premium for BTC'), and defines the output ('latest CLOSED daily residual in basis points and its regime state'). This makes the tool's purpose unambiguous and clearly distinct from the unrelated sibling tools.

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 description clearly implies when to use the tool: whenever the Bitfinex BTC cross-exchange premium is needed. It also gives concrete usage guidance for the optional `updates` parameter and notes pricing and failure behavior. It does not explicitly name alternatives or exclusions, but none of the sibling tools are related, so this is not a significant gap.

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