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

Annotations only cover read-only and closed-world, so the description carries the rest and does well: it discloses independent probing on a published schedule under a published rubric, retained captures for traceability, and the important nuance that blocked/rate-limited states are distinguished from unreachable so a defended endpoint isn't reported dead. It omits anything about the response shape or pagination, keeping it out of 5 territory.

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?

It is a single dense paragraph that spends a full clause on branding ('The Machine Commerce Observatory') before the actionable content, and the em-dash-heavy construction slows scanning. Most sentences do carry information, so it is not padding, but the core purpose is not front-loaded.

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 should explain what a 'reading' contains, but it only gestures at 'quoting what, and how fast'. The 30-day window and per-call price live in the annotation title rather than the description. For a simple one-parameter tool this is adequate, not complete.

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?

There is a single parameter and schema description coverage is 100% (the schema explains the ep_ + 16 hex id format and points to the /coverage list). The description adds no parameter detail, which matches the baseline of 3 when the schema already does the heavy lifting.

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 conveys that the tool returns observations about x402/MPP endpoints (liveness, quotes, latency), but it never plainly states that this tool returns the *history* of those readings, nor does it distinguish this from the sibling probe402_endpoint_grade. 'The Machine Commerce Observatory' leads with service branding rather than the tool's specific verb+resource.

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 gives concrete when-to-use guidance: 'Call before paying an unfamiliar endpoint, or to check whether one you use has repriced or rotated its payTo.' That is actionable context. It stops short of a 5 because it never names probe402_endpoint_grade or explains when the grade tool is the better choice.

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