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

Annotations only declare readOnly/openWorld=false, but the description adds real behavioral detail: amortizing model, optional interest-only HELOC draw phase, repayment rate change, one-time cash/financed fees, and what it returns (both phase payments, payment change, interest/cost totals). It also discloses the important edge behavior that missing fees stay unknown rather than defaulting to zero.

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-loaded with the action, then a sequence of short, purposeful sentences covering inputs, modeled behaviors, outputs, and exclusions. Dense with zero filler, though the run of negations ('No lender quote... No personal identifiers') is slightly list-like rather than flowing.

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?

There is no output schema, yet the description states what is returned (phase payments, payment change, totals), what is modeled, and what is explicitly out of scope. For a read-only, single-parameter calculation tool this leaves nothing an agent needs unresolved.

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?

With 100% schema coverage the baseline is 3, but the description adds interpretive value by grouping the inputs into 'amount, note rate and term assumptions' plus optional fee and rate-change modeling, and by reinforcing that fees must be explicit assumptions rather than inferred. It does not re-document field-level details, which is appropriate given 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+resource: 'Calculate and compare home equity loan or HELOC monthly payments.' It scopes the inputs precisely (caller-supplied amount, note rate, term) and disclaims adjacent functions ('No lender quote, eligibility decision, rate selection or APR calculation'), which clearly separates it from the rate-lookup and deposit-calculation siblings.

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?

Explicitly frames usage around caller-supplied assumptions and states what the tool will not do (quotes, eligibility, rate selection, APR), which routes the agent correctly. It stops short of naming a sibling alternative for cases where the agent actually needs live rates, so it is clear but not fully comparative.

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