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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false), so the description is not carrying that burden. It still adds genuinely useful behavior: the per-query price (0.01 USDC/query), the exact listing it applies to, and the fact that it returns fund instructions. The only friction is that the 'Buy' framing sits awkwardly beside readOnlyHint=true, though 'Returns fund instructions' clarifies no money moves here.

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?

Three short, dense sentences with no filler, and the free-alternative hint is placed early. It is front-loaded reasonably well, though the listing name and price could be trimmed without losing the agent's decision inputs.

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 one-parameter tool with no output schema, the description covers the prerequisite, the return ('fund instructions'), and the cost model, and annotations supply the safety profile. It is close to complete, with only the relationship to data_session_fund/attach_escrow left unexplained.

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 single session_id parameter is fully documented in the schema, including its origin ('from data_session_open'). The description reinforces that origin but adds no syntax, format, or constraint detail beyond the schema, so the baseline 3 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?

The description frames the tool as 'Buy per-query access to live data listings' and names the specific listing and price, but the tool name is 'data_session_funding_package' — it is not clear whether this actually purchases access or merely produces funding instructions for an already-opened session. It gestures at a verb+resource but leaves the core action ('generate a funding package for a session') ambiguous.

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 does route the agent to a free alternative ('first taste free via data_preview') and states the prerequisite (after data_session_open), which is real guidance. However, it never explains when to use this versus the closely related siblings data_session_fund and data_session_attach_escrow, leaving the most important selection decision unresolved.

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