get_message

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

Goes well beyond the readOnly/idempotent annotations: body decoding preference (plain text over HTML), a hard 60,000-character cap with a bodyTruncated marker, partIds handed off to get_attachment, and a prompt-injection warning that email content is untrusted data. These are non-obvious behavioral traits an agent must know before calling.

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 dense sentences, front-loaded with the core behavior and the routing alternative before the security caveat. Every clause — truncation limit, decode preference, partId linkage, untrusted-data warning — earns its place with no filler.

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?

Although no output schema exists, the description fully characterizes the return payload (ids, headers, body with truncation flag, snippet, attachment metadata). Combined with annotations covering the safety profile, an agent has everything needed to call and interpret this tool 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 description coverage is 100% and both parameters are documented there (account alias source, messageId pattern/provenance), so the schema carries the parameter burden. The description adds no syntax or format detail beyond what the schema already states, which is the baseline-3 case.

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 and resource ('Read one message') and enumerates exactly what is returned: ids, headers, decoded body, snippet, attachment metadata with partIds. It explicitly distinguishes itself from the sibling get_thread ('for a whole conversation'), so an agent can route without opening either schema.

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 an explicit alternative and the condition that selects it ('Use get_thread instead for a whole conversation'), and implies the messageId provenance (from search_messages, get_thread or a previous result). The agent knows when this tool is the right one versus the thread-level sibling.

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