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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds real value by drawing explicit boundaries: it does not fetch prices, charge a wallet, or submit payment, which is exactly the confusion an agent would have for an 'endpoint builder' tool.

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, zero waste. The core action leads, and the negative-scope clause follows immediately where it matters most.

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 an output schema present, return values need not be enumerated, and annotations cover the safety profile. The description completes the picture by clarifying this is a URL-construction step rather than an execution step, though it leaves the handoff to fetch unstated.

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 service enum is fully documented with per-value meanings, so the schema carries the load. The description adds no parameter-level detail such as symbol format or service selection guidance beyond what the schema already says.

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: 'Build the exact x402-protected HTTP URL for one live market-data request.' It also clarifies the output shape (method, URL, service notes, pricing docs, next steps). It doesn't name a sibling explicitly, but the negation 'does not fetch prices, charge a wallet, or submit payment' implicitly separates it from fetch.

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 only implied: build the URL, then presumably use fetch to execute it. The description never states when to prefer this over get_workflow_endpoint or get_pricing_info, and the useful 'use search_pairs first' hint lives in the schema rather than the description.

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