cal_fact_lookup

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

No annotations are provided, so the description carries the full burden. It discloses the return format ('value with source citation'), scope ('all 50 US states + DC, all county-level limits, 1-4 unit properties'), and the fact that values reset annually. It does not mention error handling or rate limits, but for a read-only lookup this is sufficient.

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 description is a single paragraph of 4 sentences, front-loaded with purpose and a list of facts. Every sentence adds value: purpose, usage rule, return format, and coverage. No wasted words.

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 lookup tool with no output schema, the description adequately explains what is returned (value with source citation) and the extent of coverage. It names the authoritative sources (FHFA, HUD, VA, Fannie/Freddie). The 6 parameters are fully covered by schema descriptions and the extra context in the description makes it complete.

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 baseline is 3. The description adds value by clarifying formatting conventions (e.g., 'lowercase with underscores' for county, 'both work' for spaces/underscores), default behavior for units, and the purpose of each parameter (e.g., va_down_payment_pct is for bracket selection). This goes beyond the schema descriptions.

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 clearly states the tool's purpose with specific verbs ('look up') and resources ('authoritative 2026 mortgage facts'). It explicitly lists the fact categories (FHFA limits, FHA limits, VA fees, etc.), distinguishing this from sibling tools like cal_scenario_pattern or cal_search_lenders, which are about scenario analysis or lender search.

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?

The description provides explicit guidance: 'Use this whenever you need a specific dollar amount, percentage, or threshold — never quote these from training-data memory'. It also warns about the difference between FHFA and FHA programs, and specifies coverage (all 50 states, county-level). This helps the agent decide when to invoke this tool over alternatives.

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