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

Annotations already declare this a safe read (readOnlyHint=true, destructiveHint=false), so the bar is lower. The description nonetheless adds real context: the data source is local config at ~/.polopan/region.json, and — importantly with no output schema present — it discloses the 'has_address' result flag that callers must branch on. It does not cover failure modes (missing/corrupt config file, no active region), which is a minor gap.

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?

Front-loads the core purpose in one sentence, then uses a labeled block for the critical usage rule; every sentence carries actionable content. The uppercase 'CRITICAL ANTI-SHORTCIRCUIT RULE' framing is slightly dramatic but defensible given the downstream branching requirement.

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?

With no output schema, the description carries the burden of explaining returns and does disclose the key 'has_address' flag plus the prefill-vs-prompt behavior. It stops short of describing the remaining address fields or the error path when no region/config is available, so it is strong but not exhaustive.

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 100%, so the single optional 'country' parameter (with code examples and default-to-active-region behavior) is already fully documented in the schema. The description's mention of the 'currently active region' restates rather than extends that semantics, so baseline 3 applies.

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?

Names a specific verb+resource (get the default delivery/shipping address) and scopes it to the active region's local configuration. It is immediately distinguishable from siblings like address.list_saved or address.delete, which operate on address collections rather than the single active-region default.

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?

Gives an explicit directive ('ALWAYS call this BEFORE generating 1-click checkout links') plus branch-specific follow-ups depending on the result, and routes to a named alternative ('address.save') when no address exists. It even states the anti-pattern to avoid (emitting a naked checkout link) and what to ask the user for instead.

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