brain_index

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

With no annotations provided, the description must disclose behavior itself. It does mention a performance caveat ('The first build on a large brain takes minutes'), implies that rebuild is a full rebuild and sync is incremental, and indicates status is a read-only check. However, it does not explicitly state that rebuild destroys the existing index or that actions may have side effects (e.g., resource usage). The transparency is good but not exhaustive.

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?

The description is three concise sentences, front-loaded with the tool's purpose and then giving actionable usage guidance. There is no filler; every sentence earns its place. It is appropriately sized for a two-parameter tool.

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 tool with two parameters, an enum, and no output schema, the description covers the key contexts: when to use each action, what they do, and timing expectations. It lacks mention of return values, but that is not critical for a management tool. The description is nearly complete for an agent to select and invoke it 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%: both action and brainId are already described in the schema (action enum values and 'never guess it' for brainId). The description adds context for when to use each action but does not provide new parameter-level semantics beyond what the schema already offers. Baseline 3 is appropriate here since the schema carries the parameter burden.

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 clearly states the tool's function: 'Manages the semantic index: status, build, refresh.' It uses a specific verb ('manages') and resource ('semantic index'), and immediately lists the three supported actions, distinguishing it from any sibling tool that does not manage the index. This is a precise, high-clarity 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?

The description provides explicit usage scenarios for each action: 'Call with action=status when brain_search complains the index is missing; with action=rebuild to build it for the first time or after changing the model; with action=sync to pull in changes (fast, new material only).' It also warns about build duration on large brains. This is exemplary when-to-use guidance, though it doesn't contrast with alternative tools since none exist for this specific task.

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