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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint, so the safety profile is covered structurally. The description adds genuinely useful non-structural context — that the call is free, does not charge credits, and does not initiate x402 payment — which prevents the agent from mistaking it for a billable or state-changing operation.

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?

Two sentences, both earning their place: the first delivers purpose and outputs, the second forecloses the most likely misreading (billing/execution). No filler, and the core purpose is front-loaded.

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 one-parameter read-only builder with an output schema present, the description need not explain return values and instead covers what an agent must know before calling: cost, side effects, and the x402 boundary. Nothing material 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% and the single enum parameter is fully documented, so the baseline is 3. The description adds no extra meaning about the product enum or how the choice affects the returned endpoint, leaving the schema to carry the load.

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 ("Build") and enumerates the concrete artifacts produced (endpoint, method, starter-credit cost, example body) for a named resource (premium Blocksize workflow). It is clearly distinguishable from execution-style siblings, though it never names or contrasts with the adjacent get_market_data_endpoint tool that covers a superficially similar need.

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?

Explicitly frames when-not to use it: "does not fetch live data, charge credits, or start x402," which tells the agent this is a preparation/metadata step rather than an execution step. It gives clear context but does not name an alternative tool for actually invoking the built endpoint or for the market-data variant.

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