vm_backup_snapshot_history

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

Annotations already mark the tool read-only, idempotent, and non-destructive, so the description adds substantial behavioral context beyond that: it returns a rollup rather than a raw list envelope, history_unavailable and coverage_note can indicate incomplete data, duplicate VM names raise an error, and the result is a lower bound on backup duration.

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 description is longer than average, but every section earns its place: scope, lower-bound semantics, return shape, failure-signal fields, duplicate-name behavior, and pointer to alternatives. It is front-loaded with the core purpose and uses formatting to make caveats scannable.

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 no output schema present, the description carries the full burden of explaining what is returned: counts, four-hour statistics, latest and longest cycles, unmatched rows, and the two fields that must be checked before reporting all-clear. It also covers the duplicate-name failure mode and directs to sibling tools appropriately.

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?

The input schema already documents all five parameters with 100% coverage, so the baseline is 3. The description adds meaningful nuance for vm_name by stating that duplicate names are refused rather than guessed, and for days by explaining that coverage_note can mean the returned window is shorter than requested.

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?

The description opens with a specific, measurable statement: 'How long backups held a snapshot open on one VM, from task history.' It names the exact resource, source of data, and one-VM scope, and it distinguishes this tool from snapshot_aging and vm_list_snapshots by pointing those tools at current snapshots.

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 explicitly routes users to vm_list_snapshots or snapshot_aging for snapshots that exist right now, while positioning this tool as the historical backup-window view. It also clarifies when the data is meaningful (image-level backup products) and warns not to treat the result as the full backup job duration.

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