brain_session_bind

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

Annotations cover the safety profile (readOnly=false, idempotent=true, destructive=false), and the description goes further: it explains the downstream effect that `end` writes only the bound slot and never the project base, enumerates all seven refusal codes, and states the replay rule. This is unusually rich disclosure and consistent with the idempotentHint.

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 key action and trigger are front-loaded in the first sentence, then constraints and refusals follow. The prose is dense with internal jargon and the refusal list is unglossed, but every sentence carries substantive information rather than filler.

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?

With an output schema present, return values need not be described, and the description adequately covers lifecycle rules, replay behavior, and failure modes. Its one real gap is the near-total absence of input-parameter meaning, which is left to a thin schema.

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%, with just `expected_client_key` documented inline. The description explains none of the three input parameters (slot_id, session_id, expected_client_key); the only parameter it references, `expected_focus_revision`, is not an input at all. It therefore fails to compensate for the coverage gap.

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 opening clause states a specific verb and resource: 'Bind an open operator session to one focus slot.' It clearly belongs to the session lifecycle family, though it never names a sibling (e.g. brain_session_end/start) to disambiguate which lifecycle call to pick, so it stops short of full sibling differentiation.

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 a clear triggering condition ('from an explicit user command') and a negative constraint ('no hook and no auto-close may invoke this lifecycle boundary'), plus once-per-session/replay semantics. What is missing is an explicit comparison to the adjacent lifecycle siblings an agent might otherwise choose.

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