Brief: where you are and what not to touch

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

Annotations already establish read-only, non-destructive, closed-world behavior, and the description usefully goes beyond them by detailing the readout's contents (focus, parked nodes, decisions, last safe point). Since no output schema exists, this enumeration is the agent's only signal about what comes back, and it covers that burden well.

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 core sentence front-loads the purpose ("Where you are ... and what NOT to touch") and the trailing sentence lands the usage instruction. It is dense but every clause maps to a distinct part of the returned brief; slightly long but not padded.

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 no parameters and no output schema, the description carries the return-value burden alone, and it does so by listing the four components of the brief. That is sufficient for an agent to call and interpret it, though the absence of any format or size cue leaves a minor gap.

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?

This is a zero-parameter tool, so there is nothing for the description to disambiguate and the baseline is 4. The description adds no misleading parameter claims.

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 names a concrete deliverable – a session brief – and enumerates its parts: focus with lineage, parked nodes with reasons, governing decisions, and the last safe point. An agent immediately understands it returns a synthesized state view rather than a filtered query. It does not explicitly contrast itself with siblings like vivac_why or vivac_find, so it stops short of a 5.

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?

"Read it before anything else when a session opens" is an explicit, actionable usage directive that tells the agent exactly when to reach for this tool. It gives no exclusions or named alternatives, so an agent must still infer why it would choose vivac_why or vivac_find at other moments.

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