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

Annotations already declare destructive/idempotent, and the description adds real value on top: what survives closure ('durable memories and journal history remain'), the authorization model ('only this session's member or a human workspace owner may close it; team read access does not grant close authority'), quota consumption, OAuth scope, and idempotent-replay semantics.

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?

Front-loaded with the core action and its sibling contrast, then tight operational facts. It is dense and runs several long sentences, but each line carries non-redundant information; only the return-field enumeration is arguably duplicative of the output schema.

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?

The output schema exists so return values need not be restated, yet the description still covers auth scope, quota, idempotency, failure/re-entry behavior, and the fact that closure is not an erase. Nothing an agent needs to invoke this correctly is missing.

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?

With 100% schema coverage the baseline is 3, but the description adds sourcing and negative-use guidance beyond the schema: where session_id comes from and 'never pass a repo slug', plus how to handle summary when a redacted checkpoint exists. These are practical constraints not present in 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?

States a specific verb and resource ('atomically closes the session') plus its trigger condition ('at a real completion or handoff'). It explicitly differentiates from the sibling engram_reflect, so an agent can distinguish the two without opening either schema.

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?

Names the alternative (engram_reflect) and the selecting condition (completion or handoff), tells the agent where to obtain session_id (start/rehydrate/list_sessions), and specifies when closure does not take effect ('a missing checkpoint or failed save leaves it active'). Guidance is explicit rather than inferred.

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