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

Goes well beyond the annotations (readOnlyHint=false, openWorldHint=true, destructiveHint=false) by disclosing that the client sees the email, that Joist records opens and signatures, that per-call confirmation is default, and that a Cotlet API key with app access is required. This is exactly the outbound/external-effect context an agent needs.

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?

Purpose is front-loaded, but the confirmation warning is stated twice ('By default you confirm each call' and 'confirm with the user before each call'), and the opening sentence is somewhat padded. Tighter phrasing would serve better.

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 4-parameter mutation with no output schema, the description covers the important human-facing behavior, external reach, confirmation requirement, and auth prerequisite. Only minor gaps (e.g. what happens on failure or duplicate sends) remain.

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 parameters are already documented (including defaults for to/message/subject). The description mostly restates that the recipient is prefilled and subject/body are editable, adding little beyond the schema. 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 (email/send) and resource (estimate or invoice document) and clarifies the action maps to Joist's 'Email button'. This distinguishes it cleanly from sibling readers like joist_get_document and creators like joist_create_estimate.

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 operating context: it sends on the user's behalf like the UI Email button, prefills the recipient, and requires confirmation by default. However, it never names explicit alternatives (e.g. create vs send) or when-not to use it, so it stops short of fully routing the agent.

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