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

Annotations already declare a safe read (readOnlyHint=true, destructiveHint=false, openWorldHint=false), and the description adds non-obvious behavioral facts: the price source, that the zero address is native WAN, and that null is returned for unpriced tokens rather than zero. That null-vs-zero rule is exactly the kind of semantic the agent can't infer from structured fields. It does not mention batching behavior or rate limits, so a 4 rather than 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?

Four short sentences, front-loaded with the resource and source, then the zero-address convention, then the historical option, then the null-price caveat. No sentence is redundant and each adds information the agent needs.

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 must convey the return shape and it largely does ('USD price ... keyed by token address', plus null semantics). It could be slightly more explicit that the response is a per-address mapping and that Wanchain is the only supported chain, but an agent has enough to call it correctly.

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 0%, so the description carries the full burden and does so for both parameters: the address is a token address keyed to a USD price, with the zero address meaning native WAN, and block selects the historical price point. It omits that addresses is a multi-item array (batch lookup) and that empty arrays are rejected, which is the only gap.

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 resource and unit precisely ('USD price per Wanchain token') and even names the data source ('OrbitWan's price table'), which no sibling tool covers. It does not explicitly contrast with nearby tools like get_token or list_tokens, so it stops short of a 5.

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?

'Pass block for the price at a past block' gives conditional guidance for the historical case, and the zero-address rule tells the agent how to price native WAN. However, there is no statement of when to reach for this tool versus get_token/list_tokens (metadata) or orbitpay_token_supplies, so routing is only implied.

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