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

Annotations only declare the safety profile (readOnly=false, openWorld=true, destructive=false). The description adds material behavior: silent skipping of guests without email, the Messaging Plus prerequisite for scheduling, the per-call confirmation default and how to disable it, and the 'reaches other people – confirm with the user' side-effect warning. That is exactly the kind of context annotations cannot supply.

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 and readable, but the opening two sentences are near-duplicates ('with a button linking to your event website' / 'with a button to your event website'), wasting space. Otherwise the operational notes are tight.

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 6-parameter, open-world send tool with no output schema, the description covers prerequisites, recipient exclusions, confirmation behavior, and auth (Cotlet API key). It does not indicate what a successful call returns or how to verify delivery, but the core calling requirements are present.

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 subject, message, guest_ids, tags, send_at, and event_id are all documented in the schema itself. The description restates the ID/tag recipient choice and the event-website button but adds no syntax or constraints beyond what the schema already conveys, so the baseline 3 applies.

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 and resource ('Sends a freeform email to the guests you pick by ID or tag'), and distinguishes the payload from transactional siblings by noting the freeform body plus an event-website button. It does not explicitly name alternative sibling tools (e.g. joy_send_rsvp_reminder, joy_send_thank_you_note), so differentiation is implicit rather than stated.

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?

Provides clear applicability conditions: recipients chosen by ID or tag, scheduling only with Messaging Plus, and that guests without an email are skipped. It lacks an explicit 'use this instead of X when...' routing against its sibling messaging tools, so it stops short of the top score.

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