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

Annotations already establish readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds genuinely useful context beyond that: the free-tier cap of 3 results, the 100-result ceiling with a key, and that the key is passed via the x-api-key header. Remaining gap is latency/caching behavior, which is minor for a screening query.

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 dense clauses with zero filler, front-loaded with the output definition before tiering and parameter constraints. Every sentence carries information the agent needs to decide and call correctly.

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 compensates by defining the returned fields (long venue, short venue, APR spread) and result caps. Combined with a fully documented schema and read-only annotations, an agent has enough to invoke it correctly; only error behavior for a missing/invalid key is unspecified.

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 baseline is 3. The description adds value by tying parameters to access tiers: limit is capped at 3 without a key, and min_oi_usd requires a key, which the schema alone does not convey. min_apr's default of 10 is only in the schema, not repeated here, which is fine.

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 computed resource: for each coin on 2+ venues, the lowest-funding (long) venue vs highest-funding (short) venue and the APR spread. That is far more than a restatement of the name and makes the calculation unambiguous. It doesn't explicitly contrast with get_funding_rates or get_funding_history, but the arbitrage framing makes the distinction inferable.

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?

Usage is implied through the tiering: free returns top 3, a Pro/trial key unlocks up to 100 results and the min_oi_usd filter. That tells the agent when the tool will be limited, but it never says when to prefer this over the sibling funding tools (raw rates, history).

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