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

Annotations already mark destructiveHint=true and readOnlyHint=false, so the mutation is known. The description adds valuable context: the shared workspace side effect (visible/editable by other callers) and the fact that it does not send. It also mentions returning the full draft. However, it does not clarify partial-update semantics (whether omitted fields are preserved or cleared), which is a meaningful behavioral gap for a patch operation.

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 with the core action front-loaded and no filler. The shared-workspace note is placed at the end, which is acceptable. The slight inaccuracy regarding 'attachments' prevents a perfect score.

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 output schema exists, so return values need not be detailed beyond the description's 'returns the full draft' statement. The shared-workspace and non-sending context are useful. However, the description omits partial-update semantics (critical for a patch tool) and includes an inaccurate 'attachments' reference, leaving an agent uncertain about field preservation. Overall, adequate but with notable gaps.

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 coverage is 100%, so parameters are fully described in the schema, earning a baseline of 3. The description's generic reference to 'recipients, subject, body' adds little beyond what the schema already provides, and the mention of 'attachments' is misleading since no such parameter exists. It does not compensate for the gap in the schema.

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 action ('Rewrites an unsent draft's recipients, subject, body or attachments') and identifies the resource clearly. It also distinguishes from sending by naming the sibling tool. However, it mentions 'attachments' which do not appear in the schema, creating a minor inaccuracy.

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?

Explicitly tells the agent when not to use it ('Still sends nothing') and names the alternative for sending. It also provides context about the shared workspace, which informs usage. It does not contrast with draft creation (post_agentmail_inbox_draft), but the purpose is clear enough.

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