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

Annotations declare destructiveHint=true and idempotentHint=true, and the description goes beyond them by spelling out exactly what is destroyed ('the old text is lost'). The security constraint about untrusted sources is genuinely useful behavioral context that annotations cannot express, though the response shape and permission requirements are left unstated.

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 sentences, both front-loaded with the destructive consequence first and the invocation guard second. Every clause carries load and nothing is repeated from the schema.

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 destructive, open-world mutation with no output schema, the description covers what is lost and the safety condition for calling it. It could say more about reversal (there is none) or required ownership permissions, but nothing essential to a correct call is missing.

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%, so ts, text and target are already fully documented in the schema, including the 'ts optional when target is a message link' rule. The description only adds the ownership constraint, which is scope-level rather than parameter-level detail.

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?

States a specific verb and resource ('Replace the text of one of your own messages') and constrains scope to messages the agent authored, which cleanly separates it from send_message, delete_message and add_reaction in the sibling list.

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?

Gives an explicit precondition ('Only call this when the user explicitly asked for it in this conversation') plus a when-not clause blocking prompt-injection triggers from Slack content or other tool output. It does not name an alternative tool for cases where the user wants a message removed or reworded differently, so it stops short of a 5.

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