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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description adds the id derivation rule, which is useful context, but says nothing about miss behavior (error vs. empty) or rate limits.

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?

One compact sentence with the resource stated first and the id format parenthetically appended. Nothing is redundant or buried.

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 one-parameter read tool whose annotations fully cover the safety profile and whose only parameter is documented, this is close to sufficient. However, with no output schema, an agent gets no hint about what the returned entry contains (village, kecamatan, postal code) or whether a miss returns an error.

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 goes beyond the schema's bare example "kp_610101" by explaining how the id is constructed: "kp_" plus the village code with dots removed. That derivation rule meaningfully improves the agent's ability to form a valid id.

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?

A specific verb ("Get") and resource ("a single postal-code entry") are stated, and "single ... by its synthetic id" implicitly separates it from kodepos_list and kodepos_search. The sibling names are not explicitly called out, so an agent must infer the lookup-vs-search split from context.

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?

Usage is only implied: take this tool when you already hold an id. There is no explicit instruction to prefer kodepos_search when starting from a name or region, and no note about what to do when the id is unknown.

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