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

The description discloses that the output is fund instructions, not a purchase confirmation, and relies on readOnlyHint/idempotentHint for the safety profile. The phrase 'Buy per-query access' could mislead an agent into thinking this tool executes a transaction, and the content or follow-up for the fund instructions is not described.

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?

The description is short and starts with the main purpose; the free-preview note and price are relevant. The 'Listing: spaceweather: ...' fragment is slightly cryptic and could read as a required input rather than an example, which keeps it from a 5.

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 read-only tool, the core invocation context (which session_id to pass) is covered by the schema and description. However, with no output schema, 'returns fund instructions' is vague about what the agent should do with the response, such as whether to follow with data_session_fund.

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 coverage is 100% and the schema already explains that session_id must come from data_session_open. The description adds no additional parameter semantics beyond what the schema provides, so it stays at the baseline.

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 action and resource: buying per-query access to live data listings, and gives a concrete listing with price. It distinguishes itself from data_preview by positioning that as the free alternative, but it does not explicitly distinguish itself from the sibling data_session_fund, leaving some ambiguity about whether it executes a purchase or only returns instructions.

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?

It gives clear sequencing ('Returns fund instructions after data_session_open') and points to data_preview as a free first step instead of paying. It does not explicitly state when to use this tool instead of data_session_fund or data_session_attach_escrow, so the guidance stops short of full exclusions.

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