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

readOnlyHint=true already tells the agent this is a safe read, so the description needed to add context such as behavior when the ID is unknown, cross-chat lookup scope, or return shape. It adds none of that, leaving the description with no value beyond the annotation.

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?

Six words with zero waste and the resource front-loaded, which is structurally clean. The brevity is efficient, though it borders on under-specification rather than tightness.

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 one-parameter read tool with no output schema, the description should at minimum hint at what comes back (a message object) and what happens on a bad ID. With annotations covering only the safety profile, the description leaves key agent questions unanswered.

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% and message_id is documented in the schema as a msg_… prefixed string, so the parameter is fully specified by structured data. The description's mention of "by its ID" only restates the schema and contributes no additional format or constraint detail.

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 fragment "One message, by its ID" implies retrieval of a single message keyed by ID, which distinguishes it from search_messages and read_chat. However, it never states an explicit verb (fetch/retrieve) and reads as a noun phrase rather than a purpose statement.

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?

There is no when-to-use guidance, no mention of when to prefer this over read_chat or search_messages, and no note about prerequisites such as needing a known message ID. The agent must infer the routing decision entirely from the name.

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