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

The annotations already establish readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description earns credit for disclosing a behavioral trait annotations cannot express: strict exact-match lookup with no fallback to nearest region or year, which tells the agent the call is brittle to bad input. What it omits is the failure mode (error vs. empty result), which matters for a strict lookup.

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?

Two short sentences with no filler. The payload contents lead and the strict-match constraint follows immediately, so the most decision-relevant information is front-loaded.

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?

An output schema exists, so the description need not explain return structure in depth, and the annotations cover safety. For a two-parameter read-only getter this is close to sufficient; the remaining gap is routing guidance among the four siblings, particularly when to use list_factor_packs to resolve a region/year before calling this.

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 description coverage is 0% for both required parameters; the properties are bare "year" (integer) and "region" (string) with no format, casing, or example values. The description partially compensates by signaling that values must match an exact bundled pack, so guessing near-misses is pointless, but it gives no syntax for either field. That is meaningful but incomplete compensation for an undocumented 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?

The description uses a concrete verb ("Return") and enumerates exactly what comes back: factors, GWP values, conversions, sources, and pack SHA, scoped to a single bundled region/year. That is far more specific than a restatement of the name. It stops short of naming a sibling, so the boundary with list_factor_packs must be inferred.

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 line "No nearest-region or nearest-year substitution" conveys an important usage condition: the caller must already hold an exact region/year pair or the call will fail. However, it never says where to obtain valid values (e.g., call list_factor_packs first) or when to prefer the bulk listing over this single-pack getter. Usage is implied rather than directed.

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