send_message_to_thread

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

Beyond the annotations, the description discloses substantial behavioral detail: it requires user authorization, refuses active threads and interactive approval policies, may load the session, returns actual settings, does not retry delivery, and advises using a stable request_id. These details add real operational context without contradicting readOnlyHint=false, destructiveHint=true, or openWorldHint=true.

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 compact and front-loaded with the primary purpose, followed by high-signal constraints and usage guidance. Every sentence carries operational weight, with no filler or repetition of schema information.

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 mutation tool with required parameters and an output schema, the description covers the full calling context: what the tool does, what preconditions it requires, what it refuses, what side effects it may have, and how to handle uncertainty. An agent has enough information to select and invoke this tool 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 has 0% description coverage, so the description must compensate. It does: thread_id maps to the 'explicitly selected idle session,' request_id is explained as needing to be stable and tied to get_operation for uncertainty, and message is understood as the single message being sent. A bit more per-parameter specificity would be ideal, but the key invocation semantics are present.

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 opens with a specific action: 'Resume the explicitly selected idle session without overrides and send one message.' It clearly identifies the resource (thread session) and the operation (send message), and goes further to distinguish itself by stating what it does not do: 'Does not steer, interrupt, set Goals, or retry delivery.' This lets an agent separate it from sibling tools such as create_worktree_thread or wait_thread.

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 gives clear context for when to use the tool: resuming an explicitly selected idle session. It also provides exclusions, such as 'Refuses an active thread and an interactive approval policy,' and suggests falling back to get_operation when uncertain. It does not explicitly name alternative sibling tools, but the when-not conditions are strong enough to guide selection.

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