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

Annotations already mark this as read-only and idempotent, and the description adds meaningful behavior beyond that: PDF failures collapse to pdf.available=False without raising, large PDFs return metadata only, contract matching is deterministic, and invoice text/PDF bytes are untrusted third-party content. This is rich, non-obvious behavioral context.

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 well-structured with a one-line summary, usage guidance, Args, and Returns sections. It front-loads the core purpose and adds only valuable details about defaults, failure modes, and security. Despite its length, every sentence earns 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?

The description covers purpose, usage, parameter semantics, return shape, failure behavior, and security considerations. An output schema exists, but the description still explains the return contract in enough detail for an agent to invoke the tool correctly and interpret results safely.

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 0%, so the description must carry the parameter documentation burden. It explains invoice_id (omit for most recent), include_pdf (default True and failure behavior), and contract_id (deterministic contract_match). However, correlation_id is not described at all, leaving one of four parameters undocumented.

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 a specific verb and resource: 'Fetch one purchase invoice with key fields and (optionally) the PDF.' It clearly distinguishes this tool from the sibling find_reconciliation_candidates by stating the inspection use case before correction or payment.

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 explicitly says when to use this tool ('Inspect a single invoice... before correcting it or applying payment') and names the alternative to prefer for matching ('Prefer find_reconciliation_candidates when the goal is matching'). This gives an agent unambiguous routing guidance.

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