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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is covered. The description adds useful behavioral context: it returns fund instructions rather than executing funding, it depends on an existing session, and it quotes a specific price. No direct contradiction with the annotations, though the word 'Buy' could be slightly misleading without the clarifying follow-up.

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 short sentences with no filler. The main action is front-loaded, the free preview alternative is mentioned efficiently, and the listing/price detail is compact but useful. Every part earns its place.

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?

There is no output schema, so the description carries the burden of explaining the return value; 'Returns fund instructions' is vague about the format, content, or how to use those instructions with data_session_fund. However, the tool has only one parameter and the workflow context from siblings helps fill some gaps, so it is adequate but incomplete.

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 schema already explains that session_id is the UUID of a session from data_session_open. The description's mention of 'after data_session_open' adds little beyond the schema's own context, so this stays at the schema-covered 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 verb and resource: 'Buy per-query access to live data listings' and names the exact listing. It also distinguishes itself from data_preview by describing it as a free taste and from data_session_open by specifying the order of operations. There is slight ambiguity about whether the tool actually executes the purchase or just returns instructions, but 'Returns fund instructions' mostly clarifies the intended action.

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 gives clear sequencing context: use data_preview first for a free taste, then data_session_open, then this tool for fund instructions. It does not explicitly say when not to use this tool versus data_session_fund or data_session_attach_escrow, but the prerequisite and flow are clear enough for basic selection.

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