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

The description adds behavior beyond annotations by clarifying that the tool 'returns fund instructions' rather than performing a direct financial transaction, which aligns with readOnlyHint and idempotentHint. It also communicates the prerequisite of an open data session and the pricing model. The word 'buy' is mildly ambiguous, but the second sentence resolves the core behavioral expectation.

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, front-loaded with the main action, and uses two sentences to cover purpose, pricing, prerequisite, and the free-preview alternative. Some of the listing detail is verbose but relevant. Overall it is efficient without significant wasted text.

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, the description covers the core prerequisite and output type ('fund instructions'), which is adequate for invocation. However, there is no output schema, and the description does not explain what the fund instructions look like or what the agent should do next (e.g., call data_session_fund or attach escrow). Some follow-up context is missing, especially given the surrounding data-session toolchain.

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%, so the parameter semantics are already fully documented: session_id is a UUID from data_session_open. The description reiterates the 'after data_session_open' prerequisite but does not materially enrich the parameter's meaning beyond the schema. This matches the baseline expected value for complete 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 names a concrete action ('Buy per-query access to live data listings') and identifies the specific listing (certfrwatch) with pricing, so the agent understands what resource this tool targets. It also distinguishes itself from the free data_preview sibling. However, 'buy' is slightly ambiguous given the tool actually 'returns fund instructions' rather than executing a purchase, and the sibling data_session_fund is not differentiated.

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 implies a workflow: try data_preview for free first, open a session, then return fund instructions for paid per-query access. It provides some sequencing guidance ('after data_session_open') and hints at the free alternative. It does not explicitly mention when to use this versus data_session_fund, data_session_attach_escrow, or data_session_query, leaving part of the selection logic to inference.

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