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

With no annotations, the description carries the full disclosure burden and does well: it enumerates the returned fields (warrant_url, py_url, md_url, fetch_when), quantifies token cost for the warrant, and describes a gating condition (seal failure blocks the .md fetch). It stops short of saying how many candidates come back, what happens for an unknown exception class, or whether a warrant is always present.

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?

Three tight sentences: purpose, return shape, then the fetch protocol with its abort condition. The routing intent is front-loaded and every sentence carries operational information.

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?

There is no output schema, so the description correctly compensates by naming all four return fields and explaining the fetch_when semantics indirectly through the warrant-first protocol. The remaining gap is edge-case behavior for unrecognized exception classes and candidate cardinality, which matters for an agent deciding whether one lookup is enough.

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 100% and the schema already supplies the meaning plus concrete examples (KeyError, TimeoutError, ValueError). The description restates 'Python exception class' but adds no format, casing, or qualification rules beyond the schema, so the baseline 3 holds.

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 names a specific verb (route/lookup) and a specific resource (a Python exception class), plus the exact target of the routing (candidate record addresses in the CorpusFetch pillar). The input domain ('Python exception class') immediately separates it from corpusfetch_lookup_symptom, which handles symptoms rather than exception classes.

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?

It gives explicit sequencing guidance for downstream work: fetch the warrant first (~220 tokens), and abort the .md fetch if the seal fails. What it does not do is state when to prefer corpusfetch_lookup_symptom over this tool; the disambiguation is left to the input type.

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