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

Beyond the annotations, the description discloses critical operational constraints: a required Last Price credential with price compute scope, a claimed workspace requirement, and a specific 403 refusal for sandbox keys from self-registration. It also describes the returned draw ordering (newest first), which is behavior an agent needs to know.

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 front-loaded with purpose, then usage, then prerequisites. The first sentence is dense with a long list of returned fields, and the phrase "each drawn, unknown or returned" is slightly cryptic, but overall there is little waste.

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 simple read-only, single-parameter tool with no output schema, the description is complete: it covers purpose, usage, authentication prerequisites, workspace claiming behavior, and the shape and ordering of returned data.

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 100%, and the schema already explains that session_id is the reservation.id from open_spend_session. The description adds no further parameter-level detail, so the baseline of 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 verb and resource ("Read a session") and then enumerates exactly what is returned: status, maximum, drawn, remaining, and draw history. This clearly distinguishes it from siblings like open_spend_session, close_spend_session, draw_session_spend, and settle_session_draw.

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 gives concrete usage contexts: "Use it to resume a run, or to find a draw to settle." This implicitly routes the agent toward settlement via settle_session_draw, but it does not explicitly name alternatives or state when not 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.