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

Annotations declare readOnlyHint=false and idempotentHint=false, and the description usefully adds that storage persists across restarts. However, with idempotentHint=false the key unanswered question is what happens when an existing name is reused (overwrite vs. duplicate vs. error) — the description is silent on this, which is the main behavioral risk.

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?

A single short sentence with no waste, front-loading the verb and resource. It is appropriately sized for the tool's simplicity, though brevity comes at the cost of the overwrite behavior noted above.

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?

An output schema exists, so return-value explanation is not required, and the persistence semantics are covered. The only material omission is collision behavior on an existing variable name, which for a non-idempotent write is worth one more clause.

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 description coverage is 100% and all three parameters (name, expression, result) are documented with types, limits and examples in the schema. The description adds no format or constraint detail beyond it, so the baseline 3 applies.

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 ("calculation to persistent workspace"), and the parenthetical defines the persistence semantics. It is distinguishable from the sibling workspace_load by contrast, though it never names the sibling explicitly.

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?

No when-to-use guidance beyond the implied durability of "persistent workspace (survives restarts)". Nothing tells the agent when saving is preferable to just recomputing with calc_expression, or what to do if a calculation shouldn't be persisted.

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