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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is fully covered. The description adds useful context about what the fetched document includes (level, casting time, range, components, duration, full description), but does not mention missing-id or not-found behavior. Overall it adds some value beyond the annotations without being richly behaviorally descriptive.

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 sentences with no wasted words. The first sentence defines the operation and what is returned; the second sentence gives the companion workflow. Everything included earns its place.

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?

This is a simple get-by-id operation with one well-documented parameter, rich annotations, and an output schema present. The description covers the essential workflow and the pointer to vault_search_spells closes the only real ambiguity: where the id comes from.

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 single parameter id is already documented in the schema as a Mongo `_id` of the vault document. The description reinforces that this id is the retrieval key and points to vault_search_spells as the source of the id, but it does not need to add more detail because the schema already fully explains the parameter.

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 states a specific verb ('Fetch'), a specific resource ('one spell document'), and the retrieval mechanism ('by id'), while enumerating the key fields returned. It is clearly distinguishable from siblings like vault_search_spells, which locates documents rather than fetching a single one.

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 names vault_search_spells as the companion tool to use first for locating the id, giving the agent a concrete workflow. This handles the main routing decision: search to find the id, then fetch by id.

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