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

Annotations already cover readOnlyHint (false), destructiveHint (false), and idempotentHint (true). The description adds valuable behavioral context: it requires an agent API key (Authorization: Bearer or X-API-Key), is not guest-callable, and involves a buyer-funded payment ('Buy per-query access'). These details are beyond the annotations and help the agent understand authentication and financial implications.

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 a compact five-sentence paragraph that front-loads the primary purpose ('Buy per-query access') before detailing prerequisites, the action, constraints, and the REST endpoint. Each sentence carries information, though the opening phrase 'first taste free via data_preview' is slightly promotional. Overall, it is appropriately sized and well-organized.

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 tool with no output schema and only three parameters, the description covers the essential aspects: what it does, when to use it (after opening a session), required authentication, and the HTTP call. It does not describe success/error responses or clarify the relationship with data_session_fund, but these are not critical for invoking the tool correctly, especially given the idempotentHint annotation. The description is adequate for the tool's complexity.

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 33% (session_id has a description; open_tx_hash and proof_escrow_id do not). The description compensates partially by stating that open_tx_hash is preferred and proof_escrow_id is an alternative, and clarifies they are references to a buyer-funded proof escrow. However, it does not explain how these identifiers are obtained or their exact roles beyond the schema constraints, so it does not fully bridge the coverage gap.

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 tool's purpose: 'Attach a buyer-funded proof escrow ... to an opened data session.' The verb 'attach' and resource 'proof escrow' are specific, and it distinguishes from siblings like data_session_open (opening) and data_session_fund (funding) by naming the escrow attachment action. It also provides the REST endpoint, further clarifying its role.

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 contextual usage guidance: it mentions 'Buy per-query access' and points to data_preview as a free alternative, implies the need for an already opened session ('to an opened data session'), and states prerequisites (API key, not guest-callable). It does not explicitly name sibling tools for comparison, but the context is sufficient for an agent to know when to use this tool.

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