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

Annotations already declare readOnly and openWorld, so the bar is lower, and the description still adds real operational context: the data source is the indexer (not on-chain), calls cost $0.002 USDC via x402 on Base/Solana/Arc, and failures are not charged. That pricing/auth-adjacent detail is exactly the kind of thing an agent can't get from the schema. It stops short of describing behavior on an invalid or missing ticker.

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?

Front-loaded with the resource and its returned fields, then the data-source caveat, then the cost. Every clause carries information, though the metric enumeration is long enough to read as an inventory rather than a summary.

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 needn't be explained, and the description covers source and cost well. However it doesn't address the conspicuous gap that 'ticker' is listed as optional (0 required params) while the description insists the tool is 'for one ticker' — an agent gets no signal on what happens if ticker is omitted or invalid.

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% and the example tickers (BTC-USD, ETH-USD) are already in the schema, so the description adds nothing new about the parameter format. Saying 'for one ticker' reinforces single-market scope but is not new semantic depth. Baseline 3 is right when the schema carries the parameter.

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-and-resource: it returns the dYdX v4 perp market for a single ticker, and enumerates exactly which fields come back (status, oracle price, 24h change, volume, trade count, funding, margins, open interest). The 'dYdX v4 (Cosmos app-chain)' qualifier separates it cleanly from sibling perp/venue tools like crypto_hyperliquid_perps_depth or crypto_binance_orderbook_depth.

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?

'Indexer data only' and 'perpetual market for one ticker' imply the use case (single-market snapshot from indexer rather than an order book or exchange API), so usage is inferable. But it never says when to pick it over the many other perp/price siblings, nor any exclusions or prerequisites. Guidance is implied, not stated.

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