Set active character

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

Annotations already indicate this is a state-changing but non-destructive operation. The description adds useful behavioral context by stating the value is validated against the account's actual character list via GGG API or poe.ninja, which implies invalid names will be rejected.

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 compact sentences, front-loaded with the tool's effect and followed by the validation behavior. Every sentence earns its place with no filler.

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 one-parameter setter with annotations covering mutation safety, the description is nearly complete. It explains the stateful effect and validation, though it does not describe success/error return behavior, which is a minor gap without an output schema.

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%, with the characterName property already described as an exact, case-sensitive string. The description does not add new parameter-level detail beyond that, so the baseline of 3 is appropriate.

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 ('Pin') and names the exact resource: which character subsequent tool calls should default to when characterName is omitted. This clearly distinguishes it from siblings like set_account_name and clear_active_build.

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?

It gives clear context for use: it changes the default character for future calls that omit characterName. It does not explicitly name alternatives or exclusions, but the usage context is unambiguous enough that an agent knows when to invoke it.

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