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

Adds context beyond the annotations: the call only mutates plan state and does not change tool access, and the required idempotent/terminal semantics of completion are spelled out. However, a large block of the disclosure discusses 'outcome.status', a field that does not exist in this tool's input schema, which muddies rather than clarifies the actual behavior.

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 instruction is front-loaded and clear, but the description is long and repeats the 'root objective vs plan item' point twice ('Do not tell the user the plan is done...'). The closing sentences about outcome.status consume space without mapping to any argument.

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?

No output schema exists, and the description adequately covers what the call does to plan state and the safety-profile context. The main gap is the unexplained `summary` field and the schema-mismatched outcome.status discussion, but an agent can still invoke the tool correctly from what is given.

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% and the description usefully compensates for conversationId and planId (omit in current conversation, must be a real UUID, never a plan item id). But it never explains the `summary` parameter, and it repeatedly references `outcome.status`, which is not present in the schema at all, so an agent may look for a parameter that does not exist.

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?

Opens with a specific verb+resource: 'Marks the active plan completed, blocked, or cancelled.' The added line 'This closes plan state only and does not alter other tool access' separates it from sibling mutators like update_plan_item and remove_plan_item.

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?

Explicitly states when to pass vs omit conversationId, forbids placeholder strings, and gives conditions for status="completed" versus blocked/cancelled when a real blocker exists. This is genuine when/when-not guidance rather than implied usage.

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