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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds genuinely new behavior: snapshots reflect post-event state, guarded values are omitted from snapshots exactly as from item data, and '1 request' signals cost. It does not mention permission or rate-limit specifics.

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?

Three compact sentences, front-loaded with what the tool returns and then the routing case. No filler; every clause adds information.

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 an output schema present, the description need not explain return shape, and it correctly focuses on the one thing an agent must know: how to obtain a stale item version. Coverage of the other resource types' prerequisites is left entirely to the schema, which is acceptable given 88% schema coverage and required-parameter enforcement.

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 88%, so the baseline is 3. The description goes slightly beyond by explaining what the snapshot contains and emphasizing that guarded values are excluded, which gives meaningful context for includeSnapshot and the returned payload semantics.

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+resource ('One event, with its snapshot') and immediately clarifies the resource scope and return payload. It also distinguishes itself from the sibling get_item by naming the version case it covers, so an agent can separate 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?

Explicitly says this is the route for reading an item version too old to fetch via get_item's version, which is a real when-to-use with a named alternative. It stops short of covering the other resource types (list/index/identity) or when not to use it, so it is clear but not exhaustive.

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