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

Annotations declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, and the description adds genuinely new context: the prior revisions are retained (a non-obvious append-versus-overwrite behavior), the operation is paid and owner-restricted, requires a subscription, and triggers no live orders or model inference. It does not describe what the response contains or how a stale-revision rejection surfaces, which keeps it off a 5.

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 behavior comes first in one tight sentence, followed by cost/ownership, effect, and access in short fragments. The final 'keyless: subscription_required with a subscribe link' phrasing is compressed to the point of awkwardness but still carries real information; nothing is redundant.

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 seven-parameter mutation with an optimistic-concurrency guard, the description covers the essential unknowns: revision retention, ownership/payment gating, and side-effect scope. With no output schema present, the absence of any statement about the return value is the remaining 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?

Schema description coverage is 100%, so all seven parameters, including the expected_revision concurrency guard and the polymorphic event_id, are already documented in the input schema. The description adds no parameter-level meaning beyond that, so the baseline of 3 applies.

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: 'Append a new revision of an existing journal note, retaining the previous revisions.' The word 'existing' plus 'revision' implicitly separates it from research_paper_append_journal (which would create a new note), but it never names the sibling, so the differentiation is inferential rather than explicit.

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?

The description supplies access preconditions ('Paid, owner-only', 'subscription_required with a subscribe link') but no direct when-to-use guidance versus research_paper_append_journal or research_paper_journal. The agent can infer that this tool is for revising and those for creating/reading, but the choice is left to inference.

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