Cancel a queued message

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

The description discloses behavioral outcomes beyond the annotations: the message ends in 'failed' state with error code 'cancelled', and it fails with 'not_queued' if the message is no longer queued. These specifics provide useful context that annotations (destructive, idempotent) do not cover, adding value without 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?

The description is two sentences with no fluff. It front-loads the core purpose, then provides outcome and the alternative, all in a compact, easily scannable structure.

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 only two parameters, no output schema, and comprehensive annotations, the description covers the essential aspects: what it does, when to use it, what happens on success and failure, and the alternative. Nothing critical is missing for an agent to invoke it 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?

Schema description coverage is 100%, so parameters are already well-documented. The description adds contextual information about the messageId parameter requiring a queued state, but does not add new parameter-specific syntax or format details beyond the schema. Baseline of 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 specific action: stopping a message that is still 'queued' from being sent. It also distinguishes itself from the sibling delete_message by specifying that delete_message is for messages that have already left the queue, making the purpose unambiguous.

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?

It explicitly says when to use this tool (when the message is still queued) and when not to (when the message already left, use delete_message instead). This direct routing between alternatives is exemplary.

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