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

Beyond the readOnlyHint annotation, the description discloses important behavioral details: the retained history scope (USASpending award rows only), the potential for fields to be 'current, absent, or nullable', and that it 'Returns dated source context.' This gives the agent a clear picture of data reliability and what to expect, which is especially valuable for a historical lookup 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 two sentences, front-loaded with the core purpose, followed by a concise caveat about data limitations and an explicit use-case sentence. Every sentence adds value and there is no fluff.

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 three parameters, one required, no output schema, and only a read-only annotation, the description adequately covers what the tool does, its limitations, and when to use it. The phrase 'Returns dated source context' hints at the output structure but does not elaborate on the response format, which is a minor gap for an agent invoking the tool.

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 already provides 100% coverage with descriptions for all three parameters. The description adds clarity on the OR relationship between 'uei' and 'cage' (though schema implies it, the description states 'using UEI or CAGE' and later 'Provide this OR `cage`' in the schema). It also contextualizes 'as_of' by linking it to the retention limitation, which goes beyond the schema 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?

The description clearly identifies the action ('Look up'), the resource ('US federal contractor record'), the temporal scope ('as of a requested date'), and the lookup keys ('UEI or CAGE'). The 'historical' framing and the explicit statement about USASpending award rows distinguish it from the sibling tool 'fonteum_lookup_contractor', which likely serves current records.

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 states when to use the tool: 'Use for historical award research or contractor change questions.' It also warns about a key limitation ('currently limited to USASpending award rows'), which helps set expectations. However, it does not explicitly name the alternative tool for current lookups or state when not to use it, though the presence of 'fonteum_lookup_contractor' implies the alternative.

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