gmail_threads_modify

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

Annotations declare readOnlyHint=false and openWorldHint=true, so the mutation nature is already signaled. The description usefully discloses the cascade side effect (label changes propagate to every message), which is real added context, but it omits permission/auth requirements and any reversal or rate-limit details.

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?

A single front-loaded sentence with no filler, though the phrasing 'and so on every message in it' is slightly awkward. It stays tight and readable.

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 mutation tool whose params are fully documented and whose safety profile is covered by annotations, the definition is adequate for correct invocation. However, with no output schema and no usage guidance, it stops short of fully equipping the agent to choose between thread- and message-level operations.

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%, with addLabelIds/removeLabelIds, id, and userId all documented in the schema including the 100-label cap. The description adds nothing beyond that, so the baseline 3 applies.

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 description states a specific verb and resource ('Modify the labels on a thread') and clarifies scope with the cascade note that it applies to every message in the thread. It is clearly distinguishable from read siblings like gmail_threads_get and gmail_threads_list, though it does not name them explicitly.

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 guidance on when to use this tool versus alternatives such as gmail_messages_get or other thread operations, nor any prerequisites or exclusions. The agent must infer usage from the purpose statement alone.

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