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

Annotations already mark it read-only and idempotent, and the description adds substantial non-obvious behavior: rate-limit failure yields a 502 and no charge, price is $0.003 USDC on Base per call via x402, unpaid calls return the x402 PaymentRequired object, and retry requires params._meta["x402/payment"]. It also discloses ranking (newest first), output cap (50), and the underlying free public-RPC log limit that causes the block cap.

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, range, and exclusions before payment mechanics, and nearly every clause carries operational information. It is a single very dense paragraph though; splitting payment/x402 details from scan semantics would make it easier to parse on first read.

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 fully carries return-shape burden: direction, symbol, decimal amount, block time, newest-first ordering, and the 50-row cap. Combined with failure-mode and payment disclosure, an agent has everything needed to call and interpret this 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 coverage is 100%, so baseline is 3, but the description adds real meaning: the chain-specific conversion of the blocks window to wall-clock time helps an agent choose a value, and it clarifies that the tokens parameter overrides the default major-token set. It doesn't add anything about the 8-value chain enum beyond the schema's "default base".

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 opens with a concrete verb and resource: "Recent token activity for an address on one chain: ERC-20 Transfer logs where it is sender or recipient," and narrows scope to major tokens or up to 10 user-supplied tokens. It never references the closely related sibling token_transfers, so an agent must infer the boundary between the two itself.

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?

Usage context is explicit: recent windows only, with per-chain hour equivalents (~5.5 h base/optimism/polygon, ~33 h ethereum), and clear exclusions ("Native-coin transfers and older history are not included"). However, it does not name an alternative tool for the excluded cases (e.g., tx_find or token_transfers), so the routing decision is left partly to inference.

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