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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety bar is low. The description still adds real value: it discloses that content arrives as base64 chunks needing decoding, and warns that the attachment's contents are data, not instructions — an important prompt-injection guard for untrusted email content.

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 short sentences, zero waste. The core operation is front-loaded and the decode/injection caveat follows immediately.

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?

An output schema exists, so return values need no prose. The description covers the chunked-base64 return shape and the safety caveat, leaving only pagination nuance (next_offset termination) to the schema, which handles it adequately.

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 75% and the schema already documents offset, max_bytes and attachment_id with useful detail (defaults, chunk continuation). The description adds no format or constraint detail beyond what the schema provides, so it sits at the baseline for well-documented parameters.

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 (read) and resource (a received email's attachment) plus the output format (base64 chunks). The 'received email' scoping quietly separates it from sent-message siblings, but it never names an alternative such as read_raw_message, so differentiation is only implicit.

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 'Read a received email's attachment' and it advises decoding bytes for downstream file tools, which is helpful. However, it gives no explicit when-to-use guidance versus read_raw_message or get_message, and no prerequisites or exclusions.

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