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

Annotations already declare idempotentHint=true and destructiveHint=false, which the description aligns with by noting 'without resetting to defaults'. The description adds permission requirements (personas:write or full permission) and the singleton storage constraint, but does not elaborate on the exact update behavior (e.g., partial vs atomic updates) beyond what is implied. No contradictions, and with annotations present, the added context is useful but not exhaustive.

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 concise, two sentences, and front-loaded with the primary purpose. The second sentence packs essential guidance about alternatives. No wasted words, though it packs many ideas into a single sentence which could be slightly clearer, but overall efficient.

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?

Given the tool's simplicity (no output schema, moderate parameter count), the description covers the essential aspects: purpose, key constraint, permissions, and alternatives. It lacks a note about possible validation errors or partial update semantics, but for this complexity level, it is fairly complete. The presence of nested objects (metadata) is not discussed, but the schema already covers that.

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%, so parameters are well documented in the schema. The description reinforces the persona_id=playbook_id constraint and the scope of updatable fields (name, system_prompt, metadata). It adds the alternative tool usage for replacing name and system_prompt together, which helps agents understand the parameter interplay, going slightly beyond the schema.

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 clearly states the tool updates a singleton persona's name, system prompt, or metadata without resetting defaults. It includes the critical constraint that persona_id must equal playbook_id, and distinguishes it from related tools like create_persona, delete_persona, and update_playbook, making its purpose unmistakable.

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 provides when to use the tool (update persona fields) and when not to, recommending create_persona when replacing both name and system prompt, delete_persona for resetting to default, and update_playbook when also changing playbook-level fields. This gives clear decision guidance relative to siblings.

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