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

Annotations indicate readOnlyHint=true and idempotentHint=true, and the description adds that the tool returns fund instructions rather than executing a purchase, which aligns with read-only behavior. It also discloses the session prerequisite. No contradiction with annotations.

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 with no fluff. The main purpose is front-loaded, and the additional context (free preview, return type) is valuable and concise.

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 single-parameter tool with high schema coverage and no output schema, the description adequately covers prerequisite (session open), return type (fund instructions), and the specific offering (listing + price). It could mention that fund instructions are likely for a subsequent step, but it's not a critical gap.

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?

The schema already fully describes session_id with 100% coverage (UUID from data_session_open). The description adds no new parameter-specific details beyond restating the prerequisite, which is already in the schema. 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 the verb 'Buy' and the resource 'per-query access to live data listings', and specifies the exact listing (Debian Security Advisories) with price. It also mentions the return (fund instructions), which clearly identifies the tool's role. It does not explicitly name sibling alternatives, but the purpose is distinct enough from generic funding tools.

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 after data_session_open ('Returns fund instructions after data_session_open') and mentions a free alternative via data_preview. However, it does not explicitly explain when to choose this tool over data_session_fund or data_session_attach_escrow, leaving some ambiguity about the exact workflow.

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