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

Annotations already declare readOnlyHint=true, destructiveHint=false, and idempotentHint=true. The description adds useful context: it returns fund instructions (rather than performing the purchase), specifies a fixed price per query, and mentions the free preview via data_preview. This exceeds annotation coverage without contradiction.

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, front-loaded with the action and cost, no filler. Efficiently conveys the listing, pricing, and prerequisite flow.

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 full schema coverage and no output schema, the description provides all needed operational details: what it does, what it returns, when to use it (after data_session_open), and available alternatives (data_preview). 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%; session_id is fully described as a UUID from data_session_open. The description repeats this prerequisite but adds no new meaning beyond the schema. Per baseline rules for full schema coverage, a score of 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?

States a specific verb ('buy') and resource ('per-query access to live data listings'), names an exact listing with cost, and differentiates from siblings by referencing data_preview and data_session_open. An agent can distinguish this from data_session_fund or data_session_query without opening schemas.

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?

Suggestively tells agents to try data_preview first ('first taste free'), and notes that fund instructions are returned after data_session_open, implying a prerequisite order. However, it does not explicitly contrast with sibling funding tools like data_session_fund or data_session_attach_escrow, leaving some ambiguity about when to pick this over those.

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