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

Annotations already declare write/idempotent/non-destructive behavior. The description adds meaningful context beyond that: the price (0.01 USDC/query) and that 'Platform-executes funding,' telling the agent payment is handled server-side rather than by the caller. It does not cover return values or failure/insufficient-funds behavior.

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?

Front-loaded with the core action and alternatives in two tight sentences. The inline listing/price example is useful but embedded awkwardly, slightly blunting the structure.

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 no output schema, a single fully-documented parameter, and annotations covering the safety profile, the description supplies the remaining essentials: cost, the free-preview alternative, and the downstream data_session_query step. Only edge-case behavior (failure modes, repeated funding) is left 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?

Only one parameter, session_id, and the schema already documents it at 100% coverage (UUID from data_session_open). The description adds nothing about the parameter, so the baseline of 3 for high schema coverage applies.

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+resource: 'Buy per-query access to live data listings,' and distinguishes itself from siblings by naming data_preview (free taste) and data_session_query (the downstream action). The hardcoded single-listing detail (unit42watch) is oddly specific and slightly muddies the generic purpose of funding a session.

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?

Gives clear context: use data_preview for a free taste, and this tool to buy access so you can then data_session_query. No explicit 'when-not' condition or mention of the adjacent funding siblings (data_session_funding_package, data_session_attach_escrow), so it stops short of full alternative routing.

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