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

Beyond the annotations, the description discloses that this performs a platform-executed funding flow (approve + createEscrowWithProof + attach) and requires authentication. It states the financial nature ('Buy', 'funding') without contradicting the readOnlyHint=false/idempotentHint=true annotations, so an agent knows this is a mutating, retry-safe operation with auth requirements.

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 purpose is front-loaded in the first clause, and all subsequent sentences carry distinct operational information: free preview route, auth requirement, platform flow, wallet conditions, and restrictions. No wasted words, despite the density of constraints.

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 one-parameter funding tool with no output schema, the description covers the operation, prerequisites, wallet context, and exclusions thoroughly. It does not explicitly state what the caller receives back or the next step after success, but the rich behavioral and usage detail makes this a minor omission.

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?

The input schema already documents the single session_id parameter at 100% coverage, including its UUID format and origin from data_session_open. The description reinforces the session context but adds no new parameter-level meaning beyond the schema, so baseline 3 is appropriate.

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 opens with a specific action 'Buy per-query access to live data listings' and identifies the resource (an existing data session), reinforced by the title 'Fund Data Session (Sandbox)'. It also distinguishes the tool from siblings by specifying it is platform-executed for testnet sandbox wallets and that user-supplied wallets should use data_session_funding_package.

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 explicit selection criteria: use for testnet sandbox wallets minted at register, while user-supplied wallets self-sign via data_session_funding_package. It also gives prerequisites (agent API key), exclusions (not guest-callable, testnet only), and points to data_preview for a free taste.

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