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

With no annotations, the description carries the full burden and does disclose two non-obvious behavioral traits: it is a paid call ($0.05 USDC / 50000 atomic) and requires no API keys. It omits rate limits, failure modes, and latency/refresh characteristics, so it is good but not complete.

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 terse telegraphic statements with no filler, and the return fields are listed compactly. Slight deduction because the pricing line is front-loaded ahead of the actual purpose, delaying the agent's answer to 'what does this do'.

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?

An output schema exists, so return values need not be explained (the description lists them anyway), and the schema fully documents the two parameters. Given no annotations, the description adequately covers cost and auth, though it could say more about paid-call failure handling or rate limits.

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 (spotPair, futuresSymbol) are already fully documented with defaults and mapping rules. The description adds the conceptual pairing of spot vs futures inputs but no syntax or format detail beyond the schema, so the baseline 3 applies.

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+resource: computes spot-vs-Kraken-Futures basis (futures mark/index/mid vs spot mid). This is clearly distinguishable from siblings like funding_snapshot and book_depth, though the differentiation is implied rather than called out.

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?

No when-to-use or when-not-to-use guidance, and no alternatives named among the sibling tools. The only qualifying context is 'Public API only — no keys', which is an auth prerequisite rather than usage guidance.

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