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

Goes well beyond the annotations by disclosing blast radius (change applies to every form, rule and report), a mandatory preview-then-confirm flow, a 10-minute token lifetime and single use. That is exactly the extra context destructiveHint/openWorldHint cannot convey.

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 action and example, then scope, then the safer alternative, then the gating workflow. Every sentence carries information, though the first-person 'I require' phrasing is slightly informal and the token details partly duplicate the schema description.

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 destructive, open-world, 7-parameter write with no output schema, the description covers impact, safeguards and timing. It stops short of naming the specific tool that produces the preview/confirmationToken, which is the one operational detail an agent still needs to infer.

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 the baseline is 3; the description earns above that by explaining the sequencing semantics of confirm and confirmationToken ('preview first, then confirm: true and its confirmationToken') rather than just restating field definitions.

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 and resource ('Sets a substitution variable to a new value') plus a concrete example (CurrMonth Mar→Apr) and the blast radius ('every form, rule and report'). It is cleanly distinguishable from the read-only sibling get_substitution_variables.

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?

Gives an explicit trigger ('when the user asks to move a period, year or scenario pointer') and points at a safer alternative (change set with plan_change and run_change). Minor weakness: plan_change and run_change are not in the sibling tool list provided, so the routing hint points at names the agent may not be able to resolve.

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