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

Annotations already declare readOnly=true, idempotent=true and non-destructive, so the safety profile is covered. The description adds genuinely new context beyond that: the exact content returned (decoded VIN spec, hiring company, category attributes with matching filters) and the cost model ('Flat 5 points per successful run'), which is information an agent cannot get from the schema or annotations.

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?

A single dense sentence front-loads the essential verb and identifier, then lists return fields and pricing with no filler. The field enumeration is long but each entry conveys real payload information, so it is not padding.

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 single-record fetch with no output schema, the description usefully enumerates what comes back, and annotations plus the stated cost round out the operational picture. Pagination is irrelevant for an ID lookup, leaving only minor gaps such as behavior on a stale or deleted posting.

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?

With one parameter at 100% schema coverage, the schema already documents that 'posting' accepts a 22-character ID or URL including an example. The description restates 'by id or URL' without adding format, normalization, or error-behavior detail, so the 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?

States a clear verb+resource ('Full Craigslist posting by id or URL') and enumerates the payload fields (title, price, body, VIN spec, hiring company, images, location, dates), which distinguishes it from generic searches. It does not name the sibling run_craigslist_postings_search or run_craigslist_postings_seller to make the detail-vs-list distinction explicit, so it stops short of a 5.

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 'by id or URL' constraint implies this is a single-record fetch rather than a search, but there is no explicit when-to-use/when-not guidance or named alternative. The 'Flat 5 points per successful run' line gives a useful cost signal that informs the decision, but routing between this and the *_search / *_seller siblings is left to inference.

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