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

Annotations already cover read-only, non-destructive and open-world, but the description adds genuinely new behavior: an unknown hash returns 404 and is uncharged, failed calls are free, and repeated calls are not free because each is billed. That last point explains why idempotentHint is false rather than contradicting it. It stops short of describing response shape or latency, which keeps it at 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?

Front-loaded with the lookup and its returned fields, then guidance, then input format, then pricing. It is dense but every clause carries information. The single long pricing sentence ('Price $0.01/call via x402 USDC or a card key (/credits), first 25 free; failed calls free') is the one place where commercial detail crowds out lookup detail.

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 compensates by listing the returned fields, and it covers the input format, the not-found case, and the cost model. For a one-parameter read tool in a large chain-prefixed family, that is everything an agent needs 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 coverage is 100% and the schema already says '0x-prefixed transaction hash (64 hex characters)', so the baseline is 3. The description earns a step up by supplying a concrete worked example hash and by stating the failure mode for a hash that isn't found, which the schema does not.

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 ('Look up an Ink transaction by hash') and enumerates exactly what is returned: sender, recipient, value in ETH, nonce, gas limit, 4-byte selector and block. It also disambiguates from its closest siblings (ink_receipt for status/fees, ink_logs for events), so an agent can pick it apart from ink_tx's neighbours 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?

Gives both positive triggers ('use to see what was sent or whether it exists') and explicit routing to alternatives with the conditions that select them: ink_receipt for success/failure and fees paid, ink_logs for emitted events. The unknown-hash/404 note further tells the agent what to expect when the lookup misses.

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