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

Annotations already supply readOnlyHint=false, idempotentHint=true, and destructiveHint=false. The description adds meaningful context beyond those: authentication requirements (Bearer/X-API-Key), the guest-call restriction, the commercial effect of the operation (per-query purchase), and the preference for open_tx_hash over proof_escrow_id. No contradiction with annotations — the mutating 'attach/buy' framing is consistent with readOnlyHint=false.

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?

Five compact sentences, each earning its place: commercial purpose, free alternative, auth requirements, mechanism with parameter preference, guest restriction, and REST endpoint. The purpose is front-loaded in the first sentence. Minor redundancy exists between the 'buy per-query access' framing and the 'attach escrow' mechanism, but the density is otherwise tight.

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 the invocation essentials well: prerequisites, target session, parameter preference, and endpoint. But with no output schema present, the lack of any mention of what a successful attach returns or how success is signaled is a real gap. It also never clarifies the relationship to data_session_fund, leaving the overall funding workflow partially unexplained.

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% — only session_id is documented in the schema. The description partially compensates by clarifying that open_tx_hash and proof_escrow_id are alternative identifiers for a buyer-funded proof escrow and that open_tx_hash is preferred. However, it does not explain where these values come from or how they relate to the escrow creation flow, leaving the two undocumented parameters under-specified.

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 action ('attach a buyer-funded proof escrow to an opened data session') and its purpose ('buy per-query access to live data listings'). It explicitly names data_preview as the free alternative, helping an agent distinguish the paid path from the free one. However, it does not differentiate this tool from the closely-related sibling data_session_fund, leaving some ambiguity about which funding mechanism to choose.

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 provides clear context: it requires an agent API key (Bearer or X-API-Key), is not guest-callable, and operates on a session opened via data_session_open (reinforced in the schema). It also hints at sequencing via 'first taste free via data_preview'. However, it gives no explicit exclusion guidance relative to sibling tools like data_session_fund or data_session_funding_package, so the when-not-to-use boundaries are incomplete.

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