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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint. The description adds valuable non-obvious behavior: 'Reports found:false rather than inventing a zero' (honesty about missing data), the cost of $0.001 USDC per call, the supported chain list, and byte-identity to a REST endpoint. These details significantly exceed what annotations provide, giving the agent critical operational knowledge.

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 description is compact and front-loaded: it states the core function first, then immediately the returned fields, followed by honest behavior, cost, supported chains, and a REST equivalent. Every sentence adds distinct value with no redundancy. It is efficient for an agent to parse.

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?

For a simple read-only tool with two well-documented parameters and an output schema, the description covers all essential aspects: what it does, what it returns, how it handles missing data, cost, and supported chains. The behavior for missing transactions ('found:false') and the pricing model are critical for agent decision-making and are included. Nothing critical is omitted.

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% (both parameters have descriptions). The description repeats the chain list from the schema and does not add new parameter-specific semantics beyond what is already documented. It does mention 'calldata length' but that is an output field, not a parameter. With full schema coverage, the baseline of 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?

The description clearly states the tool fetches a transaction by hash via eth_getTransactionByHash, and explicitly lists the decoded fields (from, to, value, nonce, gas, calldata length, inclusion block). This distinguishes it from siblings like chain_receipt (receipt data) or chain_tx_status (status checks), even though it doesn't name them.

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 implies usage by specifying the fields it returns, which suggests 'use this when you need transaction details for branching logic.' However, it does not explicitly mention when not to use it or point to alternatives (e.g., chain_receipt for receipts). The phrase 'decoded to the fields a caller branches on' provides context but lacks explicit exclusion or cross-referencing to other tools.

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