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

Annotations already cover the safety profile (not read-only, not idempotent, not destructive). The description adds genuine economic context the annotations lack - 0.01 USDC/query and a 20-queries-per-session cap - but is silent on whether opening itself costs anything, what the open_tx_hash is for, or any auth/wallet prerequisite.

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 compact sentences with the core purpose front-loaded, and the free-preview hook placed before the paid flow. The embedded listing blurb (unit42watch) is informative but slightly promotional 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 stateful purchase tool with no output schema and 0 required parameters, the description sketches the open -> fund -> query flow but never indicates what the call returns (e.g. a session handle needed for later calls), which is the key piece an agent needs to continue the 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 only 50%; listing_id and listing_slug are documented in the schema, while max_queries, open_tx_hash, buyer_address, and proof_escrow_id are not. The description partially compensates by naming a listing and the per-session query cap, but three parameters remain unexplained by both sources.

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?

States a specific action and resource: 'Buy per-query access to live data listings' / 'Open a prepaid session'. The workflow phrasing ('then fund and query') implicitly distinguishes it from data_session_fund and data_session_query, though it never names those siblings explicitly the way a 5 would.

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?

Gives a clear sequence and entry condition: try 'first taste free via data_preview', then open a session, then fund and query. This tells the agent where the tool sits in the flow, but it offers no explicit when-not-to-use or exclusion conditions.

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