Reply to Email

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

Annotations indicate a write operation (readOnlyHint=false) but are not destructive or idempotent. The description adds that it fetches the original and pre-fills fields, but doesn't specify if the reply is sent immediately, saved as draft, or any side effects beyond that.

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 sentences provide all necessary information without fluff. The first states purpose and key behavior, the second provides an alternative usage. Every sentence earns its place.

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?

The description covers the main action, pre-fill behavior, and alternative replyAll mode. Although it doesn't mention return values, an output schema exists. It could briefly note whether the reply is sent immediately or drafted, but overall it's sufficient for a simple reply tool.

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 80% (4 of 5 parameters described), so baseline is 3. The description adds minimal parameter-specific meaning beyond the schema, only mentioning that replyAll includes CC recipients.

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 clearly states 'Send a reply to an existing email,' specifying the verb and resource. It distinguishes from siblings like 'forward_email' and 'send_email' by focusing on reply-specific behavior like pre-filling To, subject, and thread references.

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 description mentions using 'replyAll' to include original CC recipients, providing guidance within the tool. However, it does not explicitly contrast with other tools like 'send_email' or 'forward_email', so cross-tool guidance is lacking.

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