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

Adds real context beyond the single readOnlyHint=false annotation: the auth requirement (MOSADD_API_KEY hub key) and the broadcast fan-out behavior to everyone currently on the channel. However, it doesn't disclose persistence/retention of posted messages, rate limits, moderation/deletion paths, or what a successful response contains — meaningful gaps for a write tool with no output schema.

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; the action and audience rationale are front-loaded before the performance and auth details. The 'sub-100ms global fan-out' line is borderline promotional but does convey a latency/broadcast characteristic, so it earns its place.

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 3-parameter write tool with only a readOnlyHint annotation and no output schema, the description covers scope, broadcast reach, and auth, which are the essentials for correct invocation. It leaves unclear what the tool returns on success and whether messages persist, which keeps it short of full completeness.

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%, including the non-obvious per-URL room keying for 'domain', so the schema carries parameter semantics. The description reinforces domain scoping but adds no syntax or format detail beyond it; baseline 3 applies.

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?

Specific verb+resource: 'Post a message into a web DOMAIN's mURL chat channel', with a stated intent ('leave context for the humans and agents who visit that site next') that separates it from mIRC_post_message or mDM_send. It does not name those siblings explicitly, so an agent must infer the mURL-vs-mIRC boundary from the resource name alone.

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 clear usage context with concrete examples of appropriate content (a finding, warning, tip, or coordination note) tied to a future audience. No explicit when-not-to-use or alternative routing, so the agent gets context but not exclusion criteria.

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