Mark a message

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

Annotations already declare readOnlyHint=false, idempotentHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered without the description. The description adds the batching behavior ('in one pass'), which is genuinely useful, but says nothing about what happens on partial failure, the dry_run preview path, or the uidvalidity resync protection beyond what the schema already states.

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?

One tightly packed sentence with zero filler; the single-vs-batch distinction and the action set are both front-loaded, and nothing is repeated.

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 6-parameter mutation tool with no output schema, the schema plus annotations carry most of the load and the description covers the core operation and batching. It stops short of explaining dry_run's role or the uidvalidity resync safeguard at the description level, but both are documented in the schema.

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 83%, so the schema already documents uid, uids, folder, dry_run and uidvalidity in detail. The description only reinforces the uid vs uids choice and maps the action names, adding marginal meaning beyond the enum and per-parameter text.

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 (Mark) and resource (message), and enumerates the supported state changes (read/unread, star/unstar) plus the single-vs-batch distinction via uid/uids. It is clear on its own, but it never names an alternative such as apply_label, so an agent must infer the boundary between flagging and labeling.

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 only implied by the parameter contrast: 'uid' for one message, 'uids' for many in one pass, which does tell an agent to batch rather than loop. There is no explicit when-to-use/when-not guidance, no mention of prerequisites like needing the message to exist in the folder, and no exclusion against sibling tools such as apply_label.

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