find_by_external_id

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It discloses a key prerequisite (ST_APP_GUID) and clarifies the matching mechanism ('externalData key/value pair'), which is useful. However, it does not describe return behavior, edge cases (e.g., not found, multiple matches), or potential side effects, leaving notable gaps for a no-annotation tool.

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 compact: two sentences, no fluff, and it front-loads the core purpose. The prerequisite and use-case are included without redundancy, making every sentence earn its place.

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 low-complexity tool with only two parameters and an output schema, the description provides adequate context: the lookup mechanism, the source of the external id, and a required app GUID. It does not explain the response when no customer is found, but the output schema likely covers return structure. Slightly more context about limits or filtering could improve completeness, so it stops short of a perfect score.

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 0%, so the description must compensate for the minimal schema. It does add meaning by explaining that 'key' and 'value' refer to an externalData pair and that the value is another system's id. Yet it lacks specifics such as accepted key formats, value types, or examples, so it does not fully bridge the coverage gap.

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 a specific action: 'Find a customer by an externalData key/value pair.' It also explains that the value is 'another system's id', which distinguishes it from the sibling 'find_customer' tool by indicating it searches through external data rather than standard customer fields.

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 clear usage context: 'Use when you hold an id from a CRM synced into ServiceTitan.' This tells the agent when the tool is appropriate, though it does not explicitly mention when not to use it or name alternative tools. This is clear guidance but lacks explicit exclusions.

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