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

With only readOnlyHint=true in annotations, the description carries most of the behavioral burden and does it well: it lists the exact returned fields per row, explains the full=true switch and its ~2 KB per-ZIP payload size, and flags the 100-item cap. It omits error behavior (e.g., unmatched or invalid ZIPs), which keeps it from a 5.

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 and batch limit are front-loaded in the first clause, and the second clause packs the return shape, the full flag, and a payload estimate with no filler. Two sentences, zero waste.

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, and the description compensates by enumerating the compact row fields and the fields returned when full=true, so the agent knows what it gets. Combined with the read-only annotation and 100% parameter coverage, nothing needed for correct invocation 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%, so baseline is 3, but the description adds meaning beyond the schema by quantifying full=true output (~2 KB per ZIP, every field) and by restating the 100-ZIP batch limit for zips. The size/field detail is genuinely incremental over the schema's terse parameter 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?

Specific verb (look up) plus resource (emission factors) with an explicit batch scope (up to 100 ZIP codes in one call). An agent can distinguish this from single-value siblings like lookup_emission_factor or lookup_by_coordinates purely from the description.

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 gives a concrete usage rule — batch up to 100 ZIPs per call and split longer lists — which tells the agent when this tool applies. It does not, however, explicitly name the alternative for single-ZIP lookups or state exclusions, so it stops short of full when/when-not routing.

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