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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety and scope are covered by structured data. The description adds only the 250-id cap, which is already in the schema's maxItems. It says nothing about whether non-member ids are omitted or returned as false, or about failure modes for invalid cohort/project ids.

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 sentences, zero filler, and the core purpose is stated first with the usage constraint second. Nothing is redundant or buried.

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 output schema, the description leaves the return shape unexplained: an agent cannot tell whether it receives a boolean per id, a subset of matching ids, or per-id status objects. For a simple read-only lookup with full schema coverage and safety annotations, this is the one remaining gap, but it is a real one.

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%, so all four parameters (userIds, cohortId, projectId, environment) are already documented, including the 1–250 range and the pointer to list_projects. The description restates the player-id and batch-limit semantics rather than adding new meaning, 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?

The description uses a concrete verb and resource: 'Check whether specific player ids belong to a cohort.' An agent can immediately tell this is a membership test rather than a listing or count. It stops short of naming the closely related siblings (get_cohort_members, get_cohort_member_count), so differentiation is implicit.

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?

'Use for bulk "is player X in cohort Y" lookups (up to 250 ids per call)' gives a clear usage context and the intended batch pattern. However, it never states when NOT to use it or names the alternative tools — notably get_cohort_members, which the agent could easily confuse with this one. Usage is implied more than routed.

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