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

Annotations already flag destructiveHint=true, so the description usefully reframes the write as a PARTIAL SAVE that leaves other v1/v2 fields untouched, and clarifies it edits schema rather than values. It does not state auth requirements or whether the UserCustomData field is replaced wholesale versus merged, a minor behavioral gap.

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?

Front-loads the critical 'PARTIAL SAVE' constraint, then the schema-vs-values distinction, then the use case. Each sentence earns its place; slight overlap between the field list and the 'SCHEMA only' restatement costs little.

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 complex nested-object mutation with annotations and a rich schema but no output schema, the description covers what is written, what is preserved, and the schema/value distinction. Nothing essential for correct invocation is missing.

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% (baseline 3), and the description adds real semantic framing beyond it: the value is a SCHEMA for per-player fields (name/type/default/visibility/writability) and is distinct from actual per-user values. It does not elaborate title_id, but the schema does.

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 (writes/save) and an exact resource scope ('ONLY the UserCustomData field of TitlePublicConfigurationModel'), and explicitly contrasts with reading actual values. An agent can distinguish it from get_user_custom_data and save_title_custom_data without opening a schema.

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?

'Use this to declare new player-specific stats, flags, or progress counters' gives clear when-to-use context, and the schema-vs-values boundary implicitly excludes reading per-user data. No explicit named alternative or when-not condition, but usage is well-contextualized.

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