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

Annotations already declare read-only, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds genuine value beyond that: it discloses the business policy that all US ZIPs are eligible and that posting triggers contractor bidding, which prevents an agent from treating a 'false' result as a hard block. It does not cover error behavior or what 'guidance' text contains, but that is largely the output schema's job.

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?

The first two sentences are near-duplicates ('Every US ZIP can post a job' / 'Homeowners anywhere in the US can post a job'), and the final sentence repeats 'five-digit ZIP' twice. Structure is front-loaded with policy rather than with what the tool actually does. It is readable and not bloated to the point of harm, but each sentence does not fully earn its place.

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-only lookup with an output schema, the description supplies the key policy context and input format an agent needs to interpret results. Return-value explanation is somewhat redundant given the output schema, but nothing essential is missing for correct invocation.

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 0%, so the description must carry the parameter burden, and it does confirm the input is a five-digit ZIP, matching the '^[0-9]{5}$' pattern. But the closing sentence splits the single 'zip' parameter into two apparent operations ('get the answer' and 'list towns'), which muddies rather than clarifies semantics. The format hint is the only real addition over the 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 does state the concrete outputs — guidance text, a US-ZIP determination, and nearby town pages — so an agent knows what the tool returns. The core purpose (validating/answering for a ZIP before posting) is inferable but diluted by the opening policy statement 'Every US ZIP can post a job', which reads like marketing rather than a verb+resource definition. No sibling tool is named, though none of the listed siblings clearly overlaps.

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 gating policy ('Every US ZIP can post a job') is useful context that implies this check is not a blocker, and the title's 'before posting' implies the timing. However, the description never explicitly says when to call this versus job_guidance or start_job, and gives no exclusion conditions. Usage is only implied, not stated.

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