Post a message to the chat thread

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

Annotations only say readOnlyHint=false, openWorldHint=true, idempotentHint=false, destructiveHint=false. The description adds valuable context: 'returns immediately without waiting for a reply,' 'Each call appends a new message and never edits or replaces an earlier one,' and 'a retry after a failure leaves a duplicate in the thread.' This exceeds what annotations convey, clarifying side effects and non-idempotency explicitly. No contradiction.

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, all informative. Front-loaded with the core action, then usage guidance, then side-effect warning. No filler or repetition.

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?

Tool is simple (3 params, no output schema). Description covers the action, return behavior, use case, alternative, and side effects (duplicate on retry). Given the sibling tools and annotations, this is 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% because every parameter has a description. The description adds nuance: for `text` it warns 'Keep credentials and secrets out of it: whoever can read the chat thread can read this,' which isn't in the schema. For `session` it explains routing and concurrency safety. It elevates beyond schema basics.

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?

Description states it 'Posts one message to this conversation's chat thread and returns immediately without waiting for a reply,' using a specific verb (posts) and resource (chat thread). It clearly distinguishes from sibling bridge_send_and_await, which waits for a reply.

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?

Explicitly says when to use: 'for a progress note or a closing remark that needs no answer.' It also gives an alternative: 'when you need the user to respond, use bridge_send_and_await instead.' This is direct when/when-not guidance naming an alternative.

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