threads_add_member

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

Annotations already indicate this is a write operation (readOnlyHint=false), non-destructive (destructiveHint=false), and idempotent (idempotentHint=true). The description adds valuable behavioral context beyond annotations by warning about rate limits for mass-adds and specifying the return structure {added, thread_id, user_id}. It does not cover permission requirements or error cases, but the provided context is sufficient for safe usage.

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 highly concise and well-structured with bold section headings (Purpose, When to use, When NOT to use, Returns). Every sentence serves a clear purpose, and the most essential information is front-loaded. There is no wasted text.

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?

Given the low complexity (2 params), the presence of annotations, and an output schema (noted but not detailed), the description covers the key aspects: purpose, usage scenarios, exclusions, and return format. It omits some details like required permissions or edge cases, but the overall context is sufficient for a straightforward operation. The description is complete enough for an agent to invoke correctly.

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 input schema already provides 100% coverage with descriptions for both parameters ('User to add', 'Thread to add the user to'). The tool description does not add any additional semantic detail about the parameters, such as how to obtain the IDs or constraints. Since the schema is complete, baseline 3 is appropriate.

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 clearly states the action: 'Add a guild user to a thread (private or public).' The verb 'add' is specific and distinguishes this from self-join tools like threads_join or removal tools like threads_remove_member. It also notes the thread type scope, leaving no ambiguity about the tool's function.

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 'When to use' section gives an explicit scenario ('loop a moderator or expert into an existing discussion'), and the 'When NOT to use' section warns against mass-onboarding, recommending an alternative action ('mention them in the parent channel instead') with a reasoning (rate limits). This provides clear decision guidance relative to alternatives.

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