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

Goes well beyond the annotations by disclosing two non-obvious behaviors: it always CCs a random boomerang+*@mail.getboomerang.ai tracking alias, and it records an email_conversations row keyed by the SES message id. It also states that workspace_id/user_id are injected from request headers, which the agent otherwise couldn't infer.

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?

Front-loaded with the action and side effects, then the usage condition, then the header-injection note. Every sentence earns its place, though the three-part structure is slightly fragmented rather than a single coherent paragraph.

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?

An output schema exists, so return values need not be explained. The description covers the send action, its hidden side effects, and injected context; combined with the side-effect disclosure it is nearly complete, with the main gap being the unexplained subject/reply_to/bcc parameters.

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 0% across 6 parameters, so the description carries the burden. It clarifies the core inputs (recipients, HTML body) and the auto-CC behavior, but says nothing about subject, reply_to, or bcc, leaving half the parameters undocumented in both places.

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?

States a specific verb+resource ('Send an HTML email to recipients via SES') and immediately distinguishes itself from siblings, none of which send email. The mechanism (SES) and the side effects are named up front, so an agent knows exactly what this does.

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?

The 'Use when' line gives clear context: 'Rudy or an internal agent must deliver an email brief or notification to a user.' It sets the triggering condition well but offers no explicit exclusions or alternative tools, since none of the siblings overlap for outbound email.

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