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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds real behavioral context beyond that: the answer is a simulated probability based on global market history, and the calculation deliberately omits taxes, government benefits and pensions, which tells the agent how far to trust the number.

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?

Purpose is front-loaded in the opening question and first clause, and the exclusions and horizon conversion follow logically. It is somewhat chatty, and the horizon arithmetic partially restates what the schema already explains, but no sentence is dead weight.

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 values need not be explained, and annotations carry the safety profile. The description covers scope, modeling basis, explicit omissions and a redirect, which is sufficient for a four-parameter calculator, though the relationship to the sibling planning tools is left unstated.

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%, so all four parameters are already documented, and the baseline is 3. The description maps the inputs in prose and supplies a worked horizon example (68 to 94 means 26 years), but the schema's own years field already says 'end age minus current age', so the added value is marginal.

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: estimates the probability a portfolio lasts through retirement from simulations on global market history, with a US-only comparison. The inputs listed (savings, spending, years, bond share) make the scope unmistakable, though it never names or contrasts itself with the sibling tools run_plan or get_plan_result.

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?

Explicit when-not guidance: it leaves out taxes, CPP/OAS, pensions and other income, and directs the person to Foresight Planner's full plan when the question turns on those. That is a clear exclusion plus an alternative, but the alternative is an external URL rather than the sibling tools, so an agent still has no stated rule for choosing this over run_plan.

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