Create thread

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

Annotations already indicate a non-read-only, non-destructive operation. The description adds meaningful behavioral context by explaining the three modes (standalone, branched, private) and the channel-type constraint. It does not disclose hidden side effects like permission requirements, but for a creation tool with these annotations, this is adequate and consistent.

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 compact sentences with no wasted words. The first sentence front-loads the core action and the three modes; the second sentence provides the critical sibling alternative. Every clause earns its place.

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?

The description covers the main behavior, all three usage modes, and the key exclusion (forum channels). It does not describe return values or prerequisites, but the lack of an output schema and the tool's relative simplicity make this acceptable. The parameter details are mostly covered by the schema descriptions.

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 71%, so the baseline is 3. The description adds value beyond the schema by explaining that message_id creates a branched thread and that private means invite-only and only works standalone. It also clarifies the channel type ('text or announcement channel'), which the schema does not specify in the parameter descriptions.

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 specific verb ('Start') with a clear resource ('a thread in a text or announcement channel'), and explicitly distinguishes itself from the sibling create_forum_post by directing forum posts elsewhere. This makes the purpose unmistakable and differentiates it from related tools.

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 provides explicit usage context: standalone threads, branched threads when message_id is given, and private threads 'when asked'. It also names an alternative tool ('use create_forum_post instead') for forum channels, clearly indicating when NOT to use this tool.

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