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

Annotations already declare readOnly=false, idempotent=true, destructive=false. The description adds genuinely useful context beyond them: the $0.001 per-call cost, 'nothing if it fails', and detailed downstream behavior of save_attachments (store space counting, skipping when full, listing non-saved attachments).

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 with the editable aspects in one dense sentence, and the parenthetical for save_attachments is informative. Minor redundancy in stating '$0.001' twice ('$0.001. Costs $0.001 per call...'), which is slightly wasteful.

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 5-param mutation tool with annotations and no output schema, the description adequately explains behavior, cost, and field effects. The only gap is no explicit statement of permissions or how to identify the target inbox, but overall it is complete enough to call correctly.

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 60%, and the description fills key gaps: it maps display_name as 'sender name' (schema has no description for it) and explains save_attachments/save_files_per_day/save_mb_per_day semantics. Only the required inbox param is left undescribed, which is self-evident.

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 (change) and resource (an inbox), and enumerates the three updatable aspects: sender name, email-in toggle, and 24h save limits. It is clearly distinguishable from create/list/release inbox siblings, though it does not explicitly name them.

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?

Usage is implied by describing what each editable field does (e.g., turning email-in on/off, raising save limits), but there is no explicit when-to-use guidance, prerequisites, or comparison against siblings like email_save_attachments or email_create_inbox.

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