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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world), and the description adds genuinely new behavioral content: what the response contains (today's-dollars balance, total contributed, growth, five-year snapshots, withdrawal-rate income). It does not disclose contribution timing assumptions (monthly vs. annual compounding, end-of-year contributions), which matters for a projection tool with no output schema.

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 trigger phrase is front-loaded and the sentence order moves from when-to-use to what-it-returns to a worked example. The trailing example is useful for sanity-checking but is somewhat redundant with the enumerated outputs, keeping it from a 5.

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 an 8-parameter projection tool with no output schema, the description covers the trigger, the full output breakdown, and a numeric example, which is enough to invoke it correctly. The remaining hole is modeling assumptions (compounding/contribution timing) that would affect interpreting the result.

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, but the description adds real linkage: it explains that contributions can be 'optionally raised each year' (annual_contribution_increase), that inflation_rate drives the today's-dollars figures, and that withdrawal_rate produces the yearly income estimate. That maps parameters to outputs in a way the schema alone does not.

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 states a specific verb and resource — 'Projects the balance at retirement from current savings and monthly contributions' — and enumerates the sub-outputs (today's dollars, total contributed, growth, 5-year balances, income estimate). It is clearly a retirement projection rather than a generic compound-interest call, though it never names a sibling calculator to contrast against.

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 opens with an explicit trigger ('Use when a user asks how much they will have when they retire') and backs it with three realistic paraphrases, which is strong routing guidance. It stops short of stating when NOT to use it or pointing to alternatives such as calculate_fire_number or calculate_savings_goal.

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