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

Annotations already mark it readOnly/idempotent; the description adds meaningful context: auth header formats (Bearer or X-API-Key), guest restrictions, and that the output is instructions plus createEscrow calldata rather than an actual charge. The opening 'Buy per-query access' is a slight tonal mismatch with readOnlyHint, but the subsequent 'Return...' phrasing makes the read-only behavior clear, so I do not treat it as a 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?

Four short sentences; the key return value is stated up front, followed by auth, non-guest restriction, and endpoint. No wasted sentences, though 'Buy per-query access to live data listings' is slightly promotional rather than purely operational.

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 this is mostly sufficient, covering auth, route, and what is returned. Without an output schema, though, the exact shape of 'funding instructions' and how the calldata should be consumed are left vague, and it does not say whether any side effects occur beyond what annotations infer.

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 covers session_id at 100% with a description pointing to data_session_open, so the description does not need to repeat it. It indirectly references the parameter in the REST path ({session_id}) but adds no new semantic detail beyond what the schema already provides.

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 concrete deliverable ('Return ... funding instructions and createEscrow calldata') for a specific resource ('data session'), and includes the REST route. It also mentions data_preview as a free alternative, which helps distinguish it from the preview path. It does not explicitly contrast itself with data_session_fund or data_session_attach_escrow, so sibling differentiation is partial.

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 conditions: requires an agent API key, is not guest-callable, and targets an opened session; implicitly this is a prerequisite step before funding/attaching. But it never explicitly says 'use this before data_session_fund/data_session_attach_escrow' or when not to use it. The free preview alternative is the only explicit routing signal.

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