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

Annotations already cover the safety profile (readOnly, openWorld, non-idempotent), and the description goes further with genuinely non-obvious operational facts: $0.003 per successful call billed via x402 USDC on Base through _meta["x402/payment"], bad input is free, and calls resolving under 2 venues (3 for a coin listed on 3+) are not charged. It doesn't discuss rate limits or what an error response looks like, so it stops short of a 5.

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?

Purpose comes first, then coverage and returned fields, then cost/payment mechanics last. The venue list and change windows each carry information an agent needs; the pricing clauses are short and load-bearing rather than 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?

There is no output schema, and the description compensates by specifying the per-venue and aggregate values returned and the three change horizons. Payment/auth requirements and billing edge cases are also disclosed, leaving nothing essential for a correct call unstated.

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% and the schema already documents alias handling (BTCUSDT, BTC-PERP, XBT, 1000PEPE, kPEPE) plus length bounds. The description adds only the constraint that exactly one coin is queried at a time, which is slight but real value over the schema, so 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?

The first clause names the exact resource and scope: open interest of one coin's perpetual futures, broken out per exchange. It enumerates the venues and the returned metrics (per-venue OI in coins and USD, share, total, 1h/4h/24h change), which cleanly separates it from siblings like perp_funding_rates, futures_basis, or perp_screener.

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 'one coin' framing implies this is the single-symbol lookup versus the multi-coin screening siblings, but that routing is left to inference. There is no explicit statement of when to prefer this over derivatives_snapshot or perp_screener, and no exclusions.

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