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

Annotations already declare the write shape (readOnlyHint=false, destructiveHint=false, idempotentHint=true), so the mutation semantics are covered. The description adds one genuinely new behavioral fact – 'Pro only', a tier precondition that will surface as an error for non-Pro users. It says nothing about what happens on repeat saves or on an invalid id, so it adds only modest context beyond the annotations.

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?

Two short sentences, front-loaded with the action and scoped by the parenthetical example. Nothing extraneous and nothing buried.

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 one-parameter, non-destructive, idempotent save with no output schema, the description plus annotations covers everything an agent needs to invoke it. A brief note on outcome (e.g. duplicate handling or error on non-Pro) would close 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 coverage is 100% and the schema itself only says 'The listing id to save.' The description adds real meaning by identifying the expected provenance of that id (a listing surfaced by find_free_stuff), which helps the agent supply a valid value rather than an arbitrary string.

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 pair ('Saves a listing ... to the user's vault') and names where the id comes from ('e.g. from find_free_stuff'). It does not explicitly distinguish itself from sibling remove_from_vault or my_vault, but the save direction is unambiguous.

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?

Gives clear context: use it when you have a listing id produced by find_free_stuff, and the 'Pro only' note signals a precondition. It stops short of stating exclusions (e.g. what to do if the listing is already saved, or which tool to use for a non-Pro user).

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