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

Annotations already declare readOnlyHint=true, and the description adds useful behavioral detail beyond that: it discloses the data sources (Census PEP, ACS), the nature of the score (z-composite), and that updates happen 'on source cadence.' It also describes the return envelope (snapshot vs optional history in the parameter schema). This goes beyond the annotations without contradicting them.

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 three sentences with no fluff: first defines the output, second gives use cases, third notes update cadence. It front-loads the most critical information and every sentence adds value. The structure is clean and scannable.

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 read-only tool with one optional parameter and no output schema, the description is complete: it states the purpose, usage triggers, output fields, geographic coverage, methodology, and update frequency. The schema handles the parameter, so no critical context is missing.

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% for the single optional 'days' parameter, which has its own detailed description in the schema (including tier requirements and fallback behavior). The tool description itself does not mention the parameter, but the schema fully covers semantics, so the baseline of 3 is appropriate.

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 specifies an exact verb ('Returns a 0-100 county population-vitality score'), defines the scope ('all 3,222 US counties'), and lists the concrete output fields (county_fips, county_name, natl_pctile, band, population, methodology_version). It also clarifies the methodology (z-composite of Census PEP 2020-2025 and ACS variables), making it unambiguous and distinct from vague sibling names.

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 when-to-use scenarios: 'Call when the user asks whether a local population is growing, young, or family-forming, or when timing site-selection, housing, retail-expansion, or market-entry decisions.' It does not state when NOT to use it or name alternative sibling tools, so it misses the full 'when-not/alternatives' bar but still gives clear context.

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