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

Annotations already mark readOnly=false and idempotent=true; the description adds meaningful auth and eligibility details (agent API key, not guest-callable) and payment context (buyer-funded escrow, per-query access). The REST endpoint also helps debugging. No contradiction with annotations.

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?

Four sentences, each adds value: commercial context, auth requirements, the core attach action, and the REST path. No filler or repetition. Exceptionally economical.

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 3-parameter tool with no output schema, the description covers prerequisites, endpoint, and parameter alternatives. It does not describe the response shape or what happens after a successful attach, but the idempotent hint and simple semantics make this a minor gap. Overall complete enough for correct selection and 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 coverage is only 33%, but the description compensates by explaining that open_tx_hash is preferred and proof_escrow_id is the alternative buyer-funded escrow reference. It doesn't fully specify the format or provenance of these identifiers, though the schema types and limits provide some help. This is above baseline for low 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 core sentence 'Attach a buyer-funded proof escrow ... to an opened data session' names the specific action and resource, and the REST path reinforces it. This distinguishes it from sibling data_session_open/query/fund, which deal with opening, querying, and funding sessions. No ambiguity about what the tool does.

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?

It provides clear prerequisites: requires an agent API key, is not guest-callable, and must target an already opened session. The 'first taste free via data_preview' hint points to a free alternative, though it doesn't explicitly contrast this attach step with the sibling data_session_fund. Context is enough to know when to invoke it.

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