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

The description discloses that the tool returns fund instructions rather than executing a payment, which is consistent with readOnlyHint=true and idempotentHint=true. It adds pricing and dependency on a prior data_session_open. However, the opening word 'Buy' could mislead an agent into thinking this tool performs a purchase, and the description relies on the annotations to clarify that it is not mutating state.

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 compact: two sentences, no redundant schema repetition, and it front-loads the core value proposition. The marketing-style phrase 'first taste free' is slightly informal but still communicates an important alternative.

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 tool with annotations already covering safety and idempotency, the description gives the essential workflow: open a session, get fund instructions, use preview for free access. It could be more explicit about what the fund instructions look like and what tool to call next, but the description is sufficient for basic invocation.

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?

The input schema covers 100% of the single parameter, session_id, with a clear description referencing data_session_open. The tool description only says 'after data_session_open' and does not add parameter-specific detail, so it neither improves nor harms the schema's already adequate documentation.

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 clearly states the tool's purpose: buying per-query access to a specific live data listing (fedwatch: US Economic Releases Index) and returning fund instructions. It names data_preview as a free alternative, which helps separate it from at least one sibling, but it does not explicitly differentiate from the similarly named data_session_fund or data_session_attach_escrow tools.

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 useful workflow context: 'after data_session_open' and 'first taste free via data_preview', which implies when to use the preview alternative. However, it does not explain when to choose this tool over data_session_fund or data_session_attach_escrow, nor what to do with the returned fund instructions.

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