op_list_users

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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, and destructiveHint=false. Beyond that, the description discloses the multi-stage fallback resolution order and the 'source' field that reports which list answered — behavior an agent genuinely needs to interpret why result sets differ. This adds meaningful context without contradicting the 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?

Three sentences, each earning its place: the core function is front-loaded in the first sentence, the second explains the critical fallback behavior, and the third clarifies a response field. There is zero filler or redundancy.

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-optional-parameter read-only tool whose safety profile is covered by annotations, the description captures the essential complexity: the fallback order, restricted-key compatibility, and the source marker. The only gap is the full response shape, but no output schema exists and the description does reveal the id and source elements, making this near-complete.

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%; the input schema already documents the project parameter, its default (OPENPROJECT_PROJECT_ID), and the 'all' sentinel. The description's phrase 'the project's assignable users' echoes the schema 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 states a specific verb and resource ('List the principals that can own a work package, with their ids'), which cleanly differentiates it from the sibling list tools (op_list_projects, op_list_work_packages, op_list_types, op_list_statuses). The 'principals that can own a work package' framing is precise and not a generic user-listing tautology.

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 fallback chain explanation ('Falls back from the project's assignable users to /principals to /users, so it works on a key that cannot read /api/v3/users') gives clear context on when this tool is the right choice — namely when credentials lack access to the users endpoint. However, it never names an alternative tool or an explicit when-not-to-use condition, so it stops short of a 5.

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