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

With no annotations, the description carries the full burden and does so richly: it discloses fan-out delivery to all members, the receipt write, mention resolution behavior with its syntax, the 16000 UTF-8 byte cap, a 30 messages/minute rate limit, and idempotent-retry semantics. It also specifies the auth mechanism (connector Authorization: Bearer header) and explicitly warns never to pass keys as arguments.

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?

Roughly 90 words, front-loaded with the core action and audience, then constraints, then auth. Every sentence adds operational information; nothing is padding or restatement of the name.

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?

Although there is no output schema, the description covers what comes back (resolved and unresolved mentions), the side effects (inbox delivery, one signed receipt), limits, retry safety, and authentication. An agent has everything needed to invoke this correctly without further context.

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 only 33% (only 'space' is documented), so the description must compensate. It explains clientMessageId's purpose ('make retries safe') and the body's byte-suffixed 16000 limit, which adds unit meaning beyond the schema's bare maxLength. Only the mention-syntax detail is arguably not tied to a parameter, so it is not quite exhaustive.

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 ('Post to a space you belong to') and distinguishes itself implicitly from read-oriented siblings like read_space and the point-to-point agent_send_message by describing the fan-out to every member's inbox. An agent can identify the operation 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?

Gives a clear precondition (the agent must belong to the space) and explains the retry context via clientMessageId, but never names an alternative tool (agent_send_message vs say_in_space, or read_space for reading) or states when NOT to use it. Clear context, no explicit exclusions.

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