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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false. The description adds behavioral context by clarifying that this operation is free, is catalog-only, and does not trigger live price fetching, account creation, or x402 payment. This goes beyond the annotations and reduces surprise.

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 concise sentences with no filler. The main action is front-loaded, and the second sentence earns its place by spelling out important non-behaviors that help with tool selection and safety expectations.

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?

The tool is simple, all three parameters are optional and well-documented in the schema, an output schema exists, and strong annotations cover safety, idempotency, and read-only behavior. The description supplies the remaining context about scope and side-effect boundaries, so nothing critical 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 schema already explains limit, offset, and service with examples for the enum values. The description does not add significant new parameter-level detail beyond repeating the 'one Blocksize service' concept, so a baseline 3 is appropriate.

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 states a specific verb and resource: 'List the supported instruments for one Blocksize service.' It also differentiates from pricing/payment tools by noting it 'does not fetch live prices, create accounts, or start x402 payment,' which helps an agent distinguish it from the 'get_pricing_info' and similar siblings.

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 provides clear context: this is free, read-only catalog metadata and explicitly lists what it does not do. It does not name alternatives or explicitly say 'use this when you need the instrument catalog,' but the negative scope is strong enough to guide an agent toward the right use case.

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