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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds valuable behavioral context by clarifying the tool 'Returns fund instructions' rather than executing a payment, and it discloses the price (0.01 USDC/query). The word 'Buy' could imply a side effect, but the instruction-generation language prevents a true contradiction with the read-only annotation.

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 and front-loaded: it states the action, points to the free alternative, identifies the listing and pricing, and clarifies the return type in two sentences. Every sentence earns its place with no redundant filler.

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 read-only annotations and full schema coverage, the description is mostly adequate. It explains the trigger (after data_session_open) and the output (fund instructions). However, it does not tell the user what to do with those instructions or how this tool relates to data_session_fund and data_session_attach_escrow, which are important next-step details for a funding workflow.

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 parameter session_id is already well described as a UUID from data_session_open. The description reinforces that this tool operates after data_session_open, but it does not add meaningful new parameter semantics beyond the schema. Baseline 3 is appropriate because the schema carries the parameter documentation burden.

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 action ('Buy per-query access') and a concrete resource ('live data listings'), and names the specific listing (npmwatch). It distinguishes itself from data_preview by framing preview as a free first taste. However, it does not explicitly separate itself from the closely named sibling data_session_fund, which creates some ambiguity about whether this tool merely returns instructions or actually processes funding.

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 usage context: use this after data_session_open, since it 'Returns fund instructions after data_session_open.' It also points to data_preview as the free alternative for a first taste. It does not explicitly mention when not to use it relative to data_session_fund or data_session_attach_escrow, but the sequential guidance is clear enough for basic invocation.

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