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

Beyond the annotations (idempotentHint=true, destructiveHint=false), the description adds auth requirements, guest-callability limits, and the 'buyer-funded proof escrow' context. It also clarifies which identifier is preferred. Nothing contradicts the annotations, and the extra context helps an agent understand the mutating, funded transaction.

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 every sentence adds useful information: commercial context, auth, the core action, guest restrictions, and the REST endpoint. It is not perfectly front-loaded — the core 'Attach...' sentence appears third — but it contains no 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 medium-complexity mutating tool with no output schema, the description covers prerequisites, auth, and the REST path. However, it omits any indication of what a successful response looks like, how an agent obtains a valid proof_escrow_id, and what happens if the session is not open or the escrow is insufficient. These gaps matter for confident 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?

Schema description coverage is only 33%, so the description needed to compensate for the two undocumented parameters. It does add the relationship that open_tx_hash is preferred over proof_escrow_id, but it does not explain when to supply one versus the other, whether both can be provided, or how these values are obtained. This is partial but not complete compensation.

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 uses a specific verb ('Attach') and resource ('buyer-funded proof escrow' to an 'opened data session'), so an agent knows what operation this is. It contrasts with data_preview ('first taste free via data_preview'), but it does not explicitly distinguish itself from the closely related data_session_fund or data_session_funding_package siblings.

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 concrete usage conditions: an agent API key is required, the tool is not guest-callable, and the escrow must be attached to an already-opened session. It also states that open_tx_hash is preferred over proof_escrow_id. However, it does not explicitly say when to choose this tool over data_session_fund or data_session_funding_package.

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