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

Annotations declare a non-read-only, non-destructive, closed-world write, so the safety profile is covered. The description adds genuinely useful behavior beyond that: the message is persisted as a versioned markdown file discoverable via query_index, requires workspace membership, and supports threading via in_reply_to. It does not state what a successful call returns, which keeps it short of a 5.

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 compact sentences, front-loaded with the core action and constraint before the parameter notes. The parameter notes duplicate the schema descriptions, which costs a little, but nothing else is wasted.

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 six-parameter mutation with no output schema, the description covers authorization (membership), default targeting (omit `to` = everyone), persistence location, searchability, and threading. The main residual gap is the response shape (e.g., the returned message id) and any rate or size limits.

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 all six parameters are already documented in the schema. The description restates the semantics of `to` and `in_reply_to` but adds no new syntax, format, or constraint beyond what the schema provides, which is the baseline-3 case.

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 ('Send a message to a workspace') plus the persistence/retrieval model ('saved as messages/<id>.md, versioned, searchable with query_index'), which distinguishes it from read_messages and query_index among the siblings. An agent can identify this as the write path for workspace messages without opening the schema.

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?

Usage context is implied by the membership constraint and the 'omit to address everyone' rule, and query_index is referenced as the way to search sent messages. However, there is no explicit when-to-use vs when-not-to-use guidance and no named alternative such as read_messages for retrieving messages, so routing among the many siblings is left to inference.

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