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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description still adds real behavioral information beyond them: the result reflects 'last found' (stored/prior state, not a fresh computation) and is ordered largest-first, and each entry is labeled by its center site.

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?

Two compact sentences with no filler, front-loaded with the definition. Slightly oblique wording ('close in meaning', 'at its center') costs it the top score, but nothing is wasted.

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 parameters, no output schema, and a read-only annotation, the description carries most of the load and does explain what the returned items conceptually are and how they are ordered. It could say more about the fields per market, but an agent can call this correctly as written.

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?

The tool takes zero parameters, so per the rubric the baseline is 4. There is nothing for the description to disambiguate on the input side, and it correctly requires no setup information.

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 gives a concrete definition of what a market is: 'groups of sites close in meaning, each named by the site at its center, largest first.' Combined with the title 'List markets' the verb+resource is clear. It falls short of 5 because it never distinguishes this from the singular sibling mttr_market or from mttr_similar/mttr_near, which plausibly return overlapping groupings.

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?

There is no statement of when to use this tool or when to prefer mttr_market, mttr_similar, or mttr_near instead. The phrase 'the markets last found' faintly implies a previously computed result set, but that is inference, not guidance.

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