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

Annotations already declare readOnlyHint=true, and the description adds genuinely new disclosure by listing the returned fields (domain, slug, status, branding, verified_at, and messages_in_window only for trending). It does not cover pagination behavior for the non-'list' modes or result ordering, which is a minor gap for a read tool.

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?

Compressed into a front-loaded block: modes first, returned fields second, follow-up tool last — no filler sentences. The slash-and-parenthesis shorthand is dense but still parseable, though it reads more like a terse spec than prose.

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?

With no output schema, the description usefully enumerates return fields, and all five parameters are documented in the schema with two enums constraining values. What's missing is modest: pagination semantics outside action='list' and ordering guarantees for trending.

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 the parameter documentation burden is already met by the schema. The description restates the default 24-hour trending window and that 'list' is status-filtered, adding little beyond what the schema's enum and property descriptions already say. 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?

Opens with a specific verb+resource ('Discovery for mURL domain channels') and immediately enumerates the three modes with what each returns, so an agent can tell trending vs list vs mine apart without opening the schema. It also names mURL_presence as the adjacent tool for a different question, which distinguishes it from siblings.

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 selection context for each action ('most active in the last N hours' vs 'paginated catalogue, status-filtered' vs 'channels you DNS-verified') plus an explicit handoff: use mURL_presence for who's-on-now. Lacks any explicit when-not-to-use or prerequisite note, so it stops short of full routing guidance.

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