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

Annotations only declare readOnlyHint/openWorldHint, but the description discloses far more: dust summarisation thresholds, the distinction between unpriced assets and zero-value assets ('Unknown is not zero'), off-page counts, and scam-token max-uint balances being flagged and withheld. This is exactly the non-obvious data-semantics context an agent needs to interpret output correctly.

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 purpose and overall dense, but it runs several long lines with some emphatic restatement ('Unknown is not zero', 'never add it to a total') that could be tightened. Every sentence is relevant, so the length is defensible rather than wasteful.

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, so the description carries the full burden of explaining the return shape, and it does: per-line chain naming, USD-descending ranking, dust counts, 'USD value unknown' for unpriced assets, and how many assets exist off-page. Nothing needed to call or interpret the tool 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 75% and the schema already documents minUsd, maxTokens and blockchains. The description still adds meaning beyond the schema by explaining how minUsd and maxTokens interact with dust summarisation and ranking, and what happens when `blockchains` is omitted.

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+scope: 'Balance of an account across many blockchains, by 0x address or ENS name, via the Ankr Advanced API indexer.' It also distinguishes itself from the sibling getBalances ('call getBalances for structured JSON'), so an agent can route between them without opening either 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?

Explicitly names the alternative (getBalances) and the condition that selects it (want structured JSON). It also gives concrete operating guidance: default top-20 listing, tune with maxTokens/minUsd, and the warning that omitting `blockchains` queries every chain and interleaves results.

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