pick_message_variant

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

Since there are no annotations, the description carries the full burden and does well: it discloses the weighted draw, the bypass behavior, silent fallback on unknown/archived variant IDs, and the NOT_FOUND return. It also describes what is returned (variant id, subject pattern, body approach, label) and the subtlety that body line is absent when no body exists. This is transparent and helps the agent anticipate edge cases.

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?

The description is a single sentence that is information-dense but not overly long. It front-loads the primary purpose and packs important nuances (return values, NOT_FOUND, body line absence) into a compact form. It could be slightly improved by adding a comma after 'project' for readability, but it is still efficient.

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 tool with 2 parameters (100% schema coverage) and no output schema, the description covers the input semantics and return value details well. It also handles an important edge case (NOT_FOUND) and explains the optional bypass parameter. The absence of an output schema is mitigated by the explicit return values. This is nearly complete for the tool's complexity.

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 schema already describes both parameters well (projectId as name/ID, variantId as specific active variant with pattern and fallback). The description adds the context of the weighted draw and the bypass semantics, which enriches the meaning of variantId. Since schema coverage is 100%, the description doesn't need to re-explain parameters but adds useful behavioral nuance.

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 ('Pick') and resource ('active message-angle variant') and clearly explains the server-side weighted draw mechanism. It also explicitly notes the return values and the NOT_FOUND case, which distinguishes it from sibling tools like list_message_variants.

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 description clearly implies when to use this tool (when you need to randomly select an active variant) and mentions the optional variantId to bypass the draw. It doesn't explicitly name alternatives or when not to use it, but the sibling tools (like list_message_variants) are distinct enough that the intended use is clear.

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