set_active_session

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

Annotations mark this as non-read-only but idempotent and non-destructive, and the description corroborates that by describing a server-side selection. Beyond the annotations it adds genuine context: the chosen session is what the budget guard charges, and budget-exhausted sessions cause the server to refuse other tool calls. It omits persistence/lifetime of the selection and whether the session_id must be validated as existing.

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?

Two sentences, no filler, and the primary action is front-loaded ahead of the consequence. Every clause earns its place.

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?

An output schema exists, so return values need not be explained. The description covers the core behavioral effect on other calls, which is what an agent most needs. Minor gaps remain around session_id provenance and whether the setting persists across calls.

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 0% for the single parameter, so the description must carry meaning for session_id. It does partially: it defines the session as the one the budget guard charges, which is more than the bare string/maxLength schema says, but it gives no format, source, or lookup guidance (e.g., how to obtain a session_id).

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?

States a specific verb+resource: selecting the session whose budget the server's guard charges. This is distinct from every sibling tool (event queue, compliance, RAG, approvals, cost tracking), so an agent can identify it without opening the schema. It stops short of 5 only because the title is null and the phrasing 'select which session' leaves the write-to-server-state aspect slightly implicit.

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?

Usage is implied rather than stated: the second sentence conveys the consequence of the selection (budget-exhausted sessions block non-guardrail calls), which gives context for when this matters. However it names no alternative, no prerequisite (e.g., whether the session must already exist), and no explicit when-not-to-use condition.

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