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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so the safety and side-effect profile is fully covered by structured data. The description adds that the payload is the raw received message (headers plus both bodies), which is a mild extra. With an output schema present and annotations doing the heavy lifting, no further behavioral disclosure is required, so this sits at baseline.

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 short sentences, front-loaded with the return payload before the usage rationale. Every sentence contributes either content or a routing cue, with no filler. Minor verbosity in the second sentence's clause structure keeps it from a 5.

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 single-parameter read tool with full annotation coverage and an output schema, the description supplies the needed purpose and two usage scenarios. Return values need not be explained since an output schema exists. The only gap is the absence of guidance on failure cases, such as what happens if no message has arrived.

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?

Only one parameter (slug) and schema description coverage is 100%, so the schema already documents that it must be a test or series letter whose message has arrived. The description adds no syntax, format, or constraint detail about the slug. Baseline 3 is appropriate when the schema fully carries parameter meaning.

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 states what the tool returns concretely: the message as received, including headers, both bodies, and source. This is specific enough to distinguish it from siblings like get_report or get_series_letters, which deal with reports and letters rather than raw received message source. It is phrased as a noun clause rather than a verb+resource, which slightly blunts the action, but the resource is unambiguous.

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?

Two concrete when-to-use scenarios are given: when a finding points at a header and the agent needs to verify what was actually sent, and when hunting a confirmation link in a welcome letter. These are clear triggering conditions. It does not name alternatives or state when not to use it, but the context is strong enough for an agent to route correctly.

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