case_open

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

The description discloses key behavioral traits: it is a write operation ([WRITE]), it returns a specific set of fields including a 'ceiling' that the agent is told to read, and it has explicit side-effect constraints in GOTCHAS: writes only under $OPS_HOME, never to a VMware system, and never over an existing case. Annotations confirm it is not read-only, not idempotent, and not destructive, and the description adds context beyond these flags (the write location and overwrite prohibition). No contradiction with annotations.

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 tightly organized into labeled sections (WRITE, WHEN, RETURNS, GOTCHAS). Each sentence earns its place: it covers purpose, usage, return shape, and side-effects in under 100 words. It front-loads the verb and resource, making it scannable for an agent. No redundancy or 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?

Given the tool's complexity (6 parameters, all documented in schema, no output schema) the description provides all necessary context: when to use it, what it returns, and critical side-effect constraints. The mention of 'ceiling' and the instruction to read it now prepares the agent for a key return value. The description is sufficient for correct invocation without requiring the agent to infer missing details.

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?

The input schema has 100% description coverage, with each parameter providing meaningful semantics (e.g., summary is used by case_plan to infer symptom category, window_start warns against invented windows, determined_by explains why it is required). The tool description itself does not add any parameter-specific meaning, but the schema already does. According to the rubric, with high coverage the baseline is 3, and that is appropriate here.

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 opens with '[WRITE] Open an investigation case — step 01, define the event.' It clearly states the action (open) and the resource (investigation case), and provides immediate differentiation from sibling incident_timeline by specifying it is for incidents to reason about rather than glance at. This is a specific, non-tautological statement of purpose.

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 contains an explicit 'WHEN:' section: 'at the start of an incident you expect to reason about rather than glance at. For a one-off lookup use incident_timeline alone.' It tells the agent exactly when to use this tool versus an alternative and sets expectations for the place in the workflow (step 01). This is clear, actionable guidance.

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