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

Annotations already declare readOnly, idempotent, non-destructive, open-world, so the safety profile is covered. The description adds genuinely non-obvious behavior: an invalid filter combination returns count 0 instead of raising an error, and the call creates/spends nothing. 'Returns { count }' largely duplicates the existing output schema, which keeps it from a 5.

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?

Three short sentences, front-loaded with purpose, then filter provenance, then the error-behavior caveat and side-effect guarantee. No filler; the only near-redundancy is the return-shape note, which is one short clause.

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 an output schema, full parameter descriptions, and rich annotations already supplied, the description covers the remaining gaps an agent needs: intent, filter id source, and the silent count-0 failure mode. Nothing material for correct invocation is missing.

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 100%, so the baseline is 3, but the description adds meaning beyond the schema by tying filter ids to an existing study retrieved via prolific_study_get, complementing the schema's pointer to prolific_filters_list. It still says nothing specific about when to set study_type, leaving that to the schema text.

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 specific verb and resource ('Count Prolific participants') plus the intent ('to check a pool is big enough'). The closing clause 'creates and spends nothing' implicitly separates it from the cost-estimation sibling prolific_study_calc_cost, so an agent can route between them without opening either schema.

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?

It states a clear usage context: counting matched screeners to verify a pool is large enough before committing. It does not name an explicit alternative or state when-not to use it (e.g., when you actually want cost, use prolific_study_calc_cost), so it falls short of full routing guidance.

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