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

Annotations already provide idempotentHint=true and readOnlyHint=false. The description adds context that this is a paid transaction (0.01 USDC/query) and that it is a prerequisite for queries, which goes beyond the annotations without contradicting them. It does not detail side effects like balance checks, but the key behavioral trait (cost and purpose) is disclosed.

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 two sentences and front-loads the core purpose ('Buy per-query access') before adding specifics like the listing and price. It is efficient, though the second sentence could be tightened by separating the listing info from the platform execution note, but it is not overly verbose.

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 low-complexity tool with one parameter and complete schema, the description covers the essential action, prerequisite (session from data_session_open via schema), and downstream use (data_session_query). It even includes extra context about the listing and price. No critical information is missing for an agent to call it correctly.

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 single parameter session_id is fully described in the schema (100% coverage), including its type, format, and source ('from data_session_open'). The tool description adds no additional parameter-specific information, so it does not improve on the schema, matching the baseline of 3 for full schema coverage.

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 verb 'Buy' and the resource 'per-query access to live data listings', specifies the exact listing (govulnwatch) and price (0.01 USDC/query), and distinguishes itself from siblings like data_session_open (open) and data_session_query (query) by describing its role as funding that enables queries.

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 context: it mentions data_preview for a free trial ('first taste free') and states that funding is required to use data_session_query. However, it does not explicitly contrast with other funding-related siblings (data_session_funding_package, data_session_attach_escrow), so it lacks a full when-not/exclusion statement.

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