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

No annotations exist, so the description carries the full burden, and it delivers substantive traits: a rate limit of 3/day, refusal of suppressed and duplicate (dedupe_key) recipients, and that no footer/logo/tracking is injected. It still omits what a successful or failed send returns and whether dedupe persists across accounts.

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?

Two tight sentences that front-load the primary action and then the operational constraints. Every clause earns its place with zero filler.

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 mutation tool with no annotations and no output schema, the description covers the key behavioral surface (rate limit, suppression, dedupe, sender identity, no tracking). It is complete enough to invoke correctly, with only minor gaps around failure/return behavior.

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 schema already documents all 7 parameters clearly. The description reinforces plain-text preference and the dedupe_key mechanism but adds little semantics beyond the schema's own parameter descriptions. Baseline 3 is appropriate.

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 a personalized outreach email') and clarifies the sending channel ('from your own address through the outreach pipeline'), which distinguishes it from generic message siblings like AddMessageTool. An agent can tell exactly what it does without opening the schema.

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 context: it prefers plain text for personalization and sends through the outreach pipeline. It does not explicitly name an alternative tool or when-not-to-use, but the 'refuses suppressed and already-contacted' constraint effectively scopes valid usage.

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