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

Goes well beyond the readOnlyHint/openWorldHint annotations: it discloses the data source (public RPCs), the per-call price ($0.001 USDC), and the failure/charging semantics ('Fails (and is not charged) if no chain's RPC answers'). It also explains token-contract provenance and bridged-USDT labelling, which an agent could not infer from structured fields.

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 what is returned, then scope exclusions, then cost/failure terms — no wasted framing. It is a dense single paragraph; the USDT/bridged-token detail is longer than most agents strictly need, which keeps it just short of a 5.

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 does explain the return shape at a high level (per-token balance, per-token USD value, and a total) and covers cost, failure, and coverage limits. It leaves the exact response field structure and partial-failure behavior (some chains failing) unstated, so it is strong but not fully complete.

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 100%, including the chains enum and its 'default all five' note, so the schema carries the parameter burden. The description reinforces the chain list and address format but adds no syntax or filtering semantics beyond what the schema already documents.

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 ('An EVM address's native coin … USDC and USDT balances') plus the exact chain set, which cleanly separates it from the generic wallet_balance and from price tools like crypto_price/token_price. An agent can identify the operation and its scope without opening the 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?

The description implicitly defines when to use it (need native/USDC/USDT balances for an EVM address across five named chains) and explicitly bounds scope by stating 'Other tokens aren't counted', which prevents misuse for arbitrary token holdings. It never names an alternative or exclusion (e.g., wallet_balance for non-EVM, token_price for single-token valuation), so it falls short of the 5 criteria.

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