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

Beyond the annotations (readOnlyHint=false, etc.), the description discloses cost structure ('First 500 lifetime writes free, then $0.01/pack'), decay timers ('context 7d, insight 90d, skill 180d, fact 365d'), the immortal=true surcharge (+$0.05), and privacy ('Vault is private — only your agent can read it'). It also states 'Requires API key,' covering authentication. No contradiction with annotations.

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 front-loaded with the primary purpose and delivers operational details (decay, pricing, immortal, privacy, pairing) in five compact sentences. It avoids unnecessary verbosity, though it repeats some type-decay information already present in the schema descriptions. This slight redundancy prevents a perfect score.

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 mutation tool with no output schema, the description covers all decision-relevant context: persistence semantics, cost implications, privacy boundary, free tier, and the companion read tool. The optional parameters are fully documented in the schema, so the description plus schema is complete enough for an agent to invoke the tool correctly and understand consequences.

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?

The input schema already covers 100% of parameters with detailed descriptions, so baseline is 3. The description adds value by mapping type values to decay durations (e.g., 'context 7d, insight 90d...') and noting the +$0.05 cost for immortal=true, which enhances the schema's parameter semantics. It does not fully compensate for all schema details, but it reinforces key parameter meanings.

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 opens with 'Write a private memory pack to your agent's personal vault,' a specific verb and target resource. It distinguishes the tool from sibling vault_query by explicitly saying 'Pair with vault_query for recall' and lists the content types (facts, insights, context, skills), 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?

It provides clear usage context: 'Pair with vault_query for recall' tells the agent when to use this write tool versus the read counterpart. It also mentions the API key requirement and the pricing structure, which are important usage conditions. It lacks an explicit 'when not to use' statement, but the context is otherwise sufficient.

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