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

Annotations already cover readOnly, idempotent, openWorld and non-destructive, and the description goes well beyond them: it discloses the data source, that proxy contracts are resolved and implementation ABI merged, what the response contains (signature lists), and the free-tier limit of 10 calls/day with paid fallback via x402 or X-API-Key. Rate limits and payment/auth mechanics are exactly the kind of behavior annotations cannot express.

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?

The capability statement is front-loaded and dense with useful specifics; the second half handles cost/auth and the serving host. Every clause carries information, though the pricing/payment sentence is tight enough that a hurried reader could miss the free-tier cap — minor structural cost, not waste.

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?

An output schema exists, so return values need no explanation; behavior, data provenance, proxy handling, cost model and auth paths are all covered. For a three-parameter read tool with full annotation and schema coverage, nothing an agent needs in order 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 description coverage is 100%, so chain, address and the `full` toggle are already documented in the schema. The description adds no extra parameter meaning (no address format rules, no chain-name expectations, no note on what `full=false` returns), so the baseline 3 applies.

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 ('Fetch a verified contract's ABI'), names the upstream source (Sourcify) and the scope of enrichment (proxy resolution, merged implementation ABI, function and event signature lists). This is clearly a read/fetch-ABI tool, distinguishable from siblings like abi_encode (encoding) or contract_read (state reads) without opening any 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?

Usage is implied by the purpose ('fetch an ABI'), and the pricing/free-tier line gives practical context for repeated use, but there is no explicit when-to-use/when-not guidance and no named alternative for cases like decoding calldata or reading contract state. An agent can infer the situation, but the definition does no routing work.

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