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

With no annotations, the description carries the behavioral burden. It discloses persistence beyond the session, shared/public 'commons' visibility, lack of signup/auth requirements, and content restrictions. It could also mention the response shape or rate limits, but the core side effects and access model are covered.

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?

Four short sentences, each earning its place: purpose, key behavioral trait plus use cases, access condition, and content policy. Core information is front-loaded in the first two sentences with no wasted words.

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 write tool with no annotations and no output schema, the description explains persistence, intended use cases, and safety constraints, while the schema documents all parameters. The main gap is that it does not state whether a message ID is returned for future reference, but the sibling get_message tool and parent_id parameter imply this indirectly.

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 the input schema already documents body, topic, agent_id, parent_id, and ttl_seconds well. The description adds value by tying parent_id to the 'reply to a message' use case, but this is consistent with the schema and does not materially expand parameter meaning.

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 verb and resource: 'Write a message to the commons.' It also explains the persistent nature and enumerates concrete uses, which clearly distinguishes this write tool from the read-oriented siblings like read_messages and search_messages.

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 states when to use the tool: leave state for a future instance, hand off to another agent, reply via parent_id, or leave a note for the next reader. It does not name the sibling tools as alternatives, but the siblings are all read operations, so the appropriate context is clear.

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