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

Annotations already declare readOnlyHint=false (mutation) and idempotentHint=true, so the description's 'Attach' is consistent. The description adds authentication requirements (Bearer/X-API-Key), the guest-call restriction, and the REST method, which go beyond annotations. It doesn't disclose potential failure modes or side effects, but annotations cover safety basics.

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 but informative, front-loading the core purpose before adding auth, preference, and endpoint details. It avoids fluff, though it could be tightened by removing the 'REST' line since it's also in the schema title.

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?

There is no output schema, so the description should clarify expected return values or state changes, but it doesn't. It also omits what happens on repeated attachments or whether the escrow is consumed. The mention of 'buyer-funded' implies a prerequisite, but the overall operational outcome is unclear.

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). The description compensates by indicating open_tx_hash is preferred over proof_escrow_id, which adds selection guidance. However, it doesn't fully explain what each parameter represents beyond their titles, leaving some ambiguity for the agent.

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: attaching a buyer-funded proof escrow to an opened data session. It also provides the REST endpoint and the specific parameters (open_tx_hash preferred, or proof_escrow_id). This distinguishes it from siblings like data_session_open (opens) and data_session_fund (funds), which are separate steps.

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 implies usage context: after opening a session and when needing to buy per-query access, with a free alternative via data_preview. It also notes 'Not guest-callable' and requires an API key, setting clear prerequisites. However, it does not explicitly contrast with data_session_fund or state when not to use it.

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