brain_session_heartbeat

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

Annotations already declare readOnlyHint=false, so the mutation is known. The description adds that this is a lifecycle boundary and only for explicit commands, but it does not explain what 'refresh' does to the session (e.g., extends timeout) or any side effects. It adds some context but not deep behavioral detail.

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, zero wasted words. The main purpose is front-loaded, and the critical usage constraint is stated immediately after. Perfectly concise.

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 mutation with no output schema, the description is somewhat bare. It does not specify behavior for a closed session, failure modes, or the return value. The agent can infer that the session must be open from the phrase 'open session', but it is not explicitly guaranteed. Given the simplicity, this is adequate but not complete.

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 50%: session_id has only a format, while expected_client_key has a detailed description. The tool description itself does not elaborate on either parameter. Since the missing session_id is self-explanatory (a UUID), the description does not need to compensate much, but it still adds no meaning beyond the schema.

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 uses a specific verb ('refresh') with a clear resource ('an open session') and immediately distinguishes itself from siblings by stating it is the only lifecycle boundary invoked by explicit user command, not by hooks or auto-close. This fully differentiates it from brain_session_start/end/resume.

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 explicitly states when to use the tool ('from an explicit user command') and, more importantly, when not to use it ('no hook and no auto-close may invoke this lifecycle boundary'). This gives the agent a clear decision rule, even though alternatives are not named directly.

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