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

Annotations already cover readOnly/destructive/openWorld, but the description adds substantive behavior beyond them: 1,000-char truncation of on-chain SVG strings, 422 for nonexistent tokens (uncharged), metadataError for unreachable metadata, and cost/charge semantics that explain why idempotentHint is false. This is unusually rich disclosure for a read tool.

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 and scope are front-loaded, followed by supported URI schemes, edge cases, alternatives, an example, and pricing. It is dense but nearly every sentence carries information; the pricing sentence is long but relevant to cost-sensitive agents.

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 still explains the return shape (name, description, image, attributes), truncation behavior, and both error channels (422 and metadataError). Nothing an agent needs to call it correctly is missing.

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 goes slightly further with a concrete example (contract=0x655C..., tokenId=1) that shows the expected value shapes, plus notes on how the returned URI may be data:/https/ipfs – helpful context for interpreting the parameters.

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+resource: reads the tokenURI of one ERC-721 token id and the JSON it resolves to, on Avalanche. It distinguishes itself from the nearest sibling by naming avax_nft_owner for owner lookups, so an agent can route without opening a schema.

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?

Explicit 'Use to show or check what an NFT is; for its owner use avax_nft_owner' names the alternative and the condition that selects it. The failed-call and pricing notes further clarify when the call is worth making.

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