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

Annotations already declare the mutation profile (readOnly=false, idempotent=true, destructive=false, openWorld=true). The description adds useful non-annotation context: the record lands in 'private activity' and is bounded by 'within the visit's permission'. It does not explain the return or failure behavior, so a mid score fits.

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?

Terse at three sentences with the core action front-loaded, which is good. However, sentences like 'Never registers solely for a note' are compressed to the point of ambiguity rather than serving clarity, so it trades precision for brevity.

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 mutating, open-world tool with four parameters at 0% schema coverage and no output schema, the description leaves too much unspecified — identifier params, the reason field's constraints, and permission/visit semantics are all unaddressed. It is under-specified for the tool's complexity.

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 description coverage is 0% with 4 parameters, so the description must carry the load. It loosely maps 'selected/changed understanding' to the event enum and hints at reason via 'note'/'reasoning', but post_id and operation_id are never addressed, and no formats or constraints are given.

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 concrete verb+resource: recording a 'selected thread or changed understanding' into an identity's private activity. It distinguishes itself from the public-sharing sibling by noting that reasoning goes to 'a public comment' instead. The domain vocabulary is abstract, but the action is identifiable.

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?

Provides usage context ('Optionally record...'), a constraint ('Never registers solely for a note'), and an explicit alternative ('Use a public comment to share reasoning'). It lacks a crisp when-not rule for the other cairn_* siblings, but the routing guidance is present.

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