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

Annotations already establish readOnlyHint=true, destructiveHint=false and closed-world scope, so the safety profile is covered. The description adds genuinely non-structured context: no credit is consumed and the feature requires the Qualisend Pro plan, which affects whether the agent should even attempt the call. It does not mention rate limits or input size limits, keeping it from a 5.

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?

The value proposition and the usage scenario are front-loaded in the first sentence, with operational notes (input source, no credit, plan) following. It is somewhat dense with parenthetical asides, but every clause carries information an agent can act on.

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?

There is no output schema, so the description must convey what comes back, and it does: transit route, per-step latency, and spam/authentication check results. For a read-only, single-parameter tool with annotation coverage and an explicit plan/cost note, nothing an agent needs to call it correctly is missing.

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?

With a single parameter at 100% schema description coverage, the schema already documents 'raw'. The description reinforces this with 'Paste the message source / Show original', which adds practical guidance for locating the value but no new format or syntax detail. This is the expected baseline when the schema carries the load.

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 names a specific verb and resource ('Read the hidden technical details of an email (its headers)') and enumerates the concrete outputs: route taken, per-hop timing, and spam/authentication results. This clearly separates it from siblings like verify_email and check_blacklist, which do not analyze an existing message's transit path.

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 a clear triggering scenario ('handy for figuring out why a message was slow or went to spam') and tells the agent what input to supply ('Paste the message source / Show original'). It does not explicitly name alternatives or state exclusions, so it stops short of a 5.

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