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

Annotations already indicate readOnly, idempotent, and non-destructive behavior, and the description adds substantial context beyond them: unpriced tokens return null rather than a substituted price, unpaid calls return a payment challenge, and no-data calls are never settled. These edge cases are crucial for correct invocation and interpretation.

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 dense but every sentence serves a purpose: it identifies the tool, its use case, its output, its relation to a sibling tool, null behavior, cost model, and equivalent HTTP route. No filler or repetition exists, and the most important identifying information is front-loaded.

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 paid, read-only data tool with no output schema, the description covers the essential context: input format, output fields, pricing failure mode, null behavior, and alternative routing. An agent has enough information to call it correctly and interpret results in the context of the sibling tools.

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%, so the baseline is 3. The description adds value by restating the chain:address / coingecko:id addressing convention and clarifying the search_width semantics by explaining that tokens not priced within that window return null. It slightly reinforces the schema without fully compensating for the missing required-field indication, but it remains useful.

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 ('Price arbitrary on-chain tokens') and resource ('DefiLlama's coins API'), and explains the addressing scheme and output fields. It also explicitly distinguishes itself from the crypto spot-price tool, so an agent can tell them apart without inspecting schemas.

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 gives a clear use case ('value a DeFi position holding tokens no exchange lists') and an explicit when-not-to-use statement with the alternative tool ('use the crypto spot tool for a plain price of a major asset'). It also explains relevant cost and failure behavior, which helps the agent decide whether to call this tool.

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