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

Adds substantial context beyond the annotations: the 8 KB calldata cap, revert behavior (422 with reason, uncharged), pricing ($0.01/call via x402 or card key, first 25 free), and that failed calls are free. Crucially it explains why a read-only tool is not idempotent — every call is charged, so repeats aren't free — reconciling idempotentHint=false with readOnlyHint=true.

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-loads the verb, resource and mechanism, then usage rule, then limits, errors, and pricing in a short paragraph with zero filler sentences. The pricing detail earns its place because it drives the non-idempotency reasoning.

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 tells the agent what comes back (raw return data, to be ABI-decoded) and what a failure looks like (422 plus revert reason). For a three-parameter read tool with full schema coverage, nothing needed 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 baseline is 3, but the description adds real value: a concrete worked example (to=0x078D7..., data=0x18160ddd), the requirement to decode raw return data with the function's ABI, and the 8 KB calldata limit. It does not explain the optional `from` parameter, leaving that entirely to the schema.

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 ("Read-only contract call on Unichain (eth_call)") plus scope (latest block, raw return data, no transaction/gas). It explicitly differentiates from siblings by saying to use it for view functions that have "no dedicated tool," which separates it from unichain_token_balance, unichain_storage, etc.

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 a clear selection rule: use for any view function lacking a dedicated tool, and it points to the ABI for decoding. It does not name concrete alternatives (e.g. "use unichain_token_balance for ERC-20 balances"), so the agent must infer sibling boundaries from the catalog, but the routing condition itself is explicit.

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