Set active character

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

Annotations already establish that this is a mutating (readOnlyHint=false), non-destructive operation. The description adds the behavioral details that input is validated before the value is persisted, but it does not disclose failure behavior or whether a previously set active character is overwritten.

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 a single, focused sentence with no filler. The core action, resource, and purpose are front-loaded, making it easy to parse quickly.

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 simple three-parameter setter with no output schema, the description and input schema provide enough information to call the tool successfully. It lacks explicit return or error-handling details, but the basic intent and persistence behavior are clear.

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 only 33%: only 'server' has a description, while 'name' and 'serverRegion' rely on type and enum. The description does not meaningfully explain these parameters beyond labeling the resource as a character, so it does not compensate for the low schema coverage.

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 uses a specific verb phrase, 'Validate and persist,' and clearly identifies the resource as the default character. It also states the scope of use ('character discovery and ranking tools'), which distinguishes it from sibling tools like get_active_character and clear_active_character.

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 implies the tool is used before character discovery or ranking operations by saying the character is 'used by character discovery and ranking tools,' but it does not explicitly state when to call it or contrast it with alternatives such as get_active_character or clear_active_character.

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