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

Annotations already declare readOnly, idempotent, non-destructive and openWorld, so the safety profile is covered; the description adds real operational context: endpoint path, availability on all plans including free, and a cost of 1 request unit per call. It also sketches the response (JSON in Turkish with source and `guncelleme`), though it says nothing about what happens for an unassigned or malformed code.

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-loaded with the return value, then usage, then operational metadata in a compact second block — no filler sentences. The endpoint/cost/plan cluster is slightly reference-manual in tone but each item earns its place for an agent deciding whether to call.

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 with no output schema, the description covers input meaning, return content, cost, and plan availability. The remaining gap is error/not-found behavior for an invalid or unassigned postal code, which an agent would otherwise have to discover at call time.

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% and the `kod` property already carries the pattern ^\d{5}$ and an example '81850'. The description's "5-digit" restates the schema rather than extending it, so the baseline of 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?

"Returns the province, district and neighbourhoods that use a 5-digit Turkish postal code" gives a specific verb (returns) plus the exact resource and the three fields resolved. It also separates this tool from the reverse-direction sibling by naming uc_ara.

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?

States the use case ("validate or auto-fill address forms") and explicitly routes the opposite lookup direction to uc_ara with the search phrase 'posta kodu ara'. Both when-to-use and the alternative are spelled out rather than implied.

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