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

With no annotations, the description carries the full burden and does disclose the key behavioral trait: data survives termination and is retrievable by the same id. It omits retention/TTL, size limits (only 'keep it small' in the schema), whether entries are namespaced or shared, and what a save returns.

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 tight sentences with the purpose and durability guarantee front-loaded; every clause (survives termination, retrieve by id, ephemeral runtime) carries distinct information.

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 two-parameter write tool with no output schema and no annotations, the description covers what it does, why it matters, and how to retrieve the data. Remaining gaps (retention period, size cap, overwrite behavior) are modest and partly handled by the 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%, so both parameters are already documented, including the reuse-id-to-update semantic. The description reinforces the read-back-by-id pattern but adds no syntax, format, or constraint detail 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?

States a specific verb ('save') and resource ('durable key-value store') plus the content types it accepts (working state, scratchpad, context summary). It doesn't explicitly name or differentiate from siblings such as handoff_dead_drop, though the persistence framing is distinct enough to separate it in practice.

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 avoid losing progress when your runtime is ephemeral' gives a clear triggering condition, and the mention of container termination/sandbox recycle/session reset sharpens it. No explicit when-not guidance or named alternative is given.

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