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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false — so the agent knows this is a safe, repeatable read. The description adds the pricing detail (0.01 USDC/query) and the free-preview alternative, which is genuinely useful beyond annotations. But it fails to state what 'returns fund instructions' actually means (is this a payment endpoint, a quote generator, or a status reader?) and doesn't clarify whether the price is quoted, charged, or reserved.

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 sentences are compact, but the phrasing is telegraphic to the point of ambiguity — 'returns fund instructions' is load-bearing and undefined. The 'Listing:' fragment reads like a data leak from an internal catalog. Front-loading the value (per-query access) is good; the rest could be clearer without being longer.

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 payment-adjacent tool with no output schema and only read-style annotations, the description doesn't reveal the return shape or what 'fund instructions' contains. The pricing context is useful. But given the dense sibling set (fund, attach_escrow, funding_package, query, preview), the description leaves the agent unsure which sibling to pick. Adequate but with clear gaps.

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 itself explains the session_id originates from data_session_open. The description reinforces this dependency ('after data_session_open') but adds little new. With one parameter fully documented at 100% coverage, the schema carries the load; the description doesn't need to compensate.

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 establishes the objective — buying per-query access to live data listings and returns payment/funding instructions — but the name 'data_session_funding_package' implies creating a bundle or funding package, which the description never explains. 'Returns fund instructions after data_session_open' is the only concrete behavioral claim, and it's unclear whether this tool itself creates a package or just generates instructions. An agent can't tell from the description whether there's a difference between this and data_session_fund.

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 names data_preview as the free-trial entry point and mentions data_session_open (a sibling), but doesn't state when to choose this over data_session_fund or data_session_attach_escrow. The ordering hint ('after data_session_open') is implicit rather than stated as a prerequisite. The schema's own description mentions 'funding-package / attach / query' as a triad, further muddying which is the right sibling.

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