epost_letter_pdf

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

With no annotations, the description carries the full burden and does disclose meaningful behavior: 'Nothing is written where this server runs' (read-only), the 10 MB cap (EPOST_PDF_MAX_BYTES), that the single output field content_base64 holds either a PDF or an EML, and the format codes. It omits auth requirements and rate/error behavior, keeping it short of a 5.

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 key fact (document of one letter by letter_id as base64) is front-loaded, and the following sentences each add distinct information (formats, output field, no writes, size cap). It is dense and reads as chained clauses rather than clean sentences, but there is little outright waste.

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 and no annotations, so the description must explain returns and safety, and it does: it names content_base64, the pdf/eml formats, the read-only nature, and the size limit. Auth/permission context is the remaining gap, but overall it is complete enough to call correctly.

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% for the single required letter_id. The description adds that it identifies one letter located either in the inbox or filed in Storage, which is useful scope beyond the bare schema type, but it gives no identifier syntax or example. Modest added value above the schema.

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 states a specific resource (the document of one letter, in inbox or Storage, keyed by letter_id) and a specific output (base64 in the answer). It is clear for an agent, but it never distinguishes itself from close siblings like epost_download_letter, epost_get_letter, or epost_letter_text, so routing among them is left to inference.

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?

'for a client that decodes the payment QR code or keeps a backup without a shared disk' implies the use case and the read-only/no-disk condition. However, no alternative is named and there are no explicit exclusions, so an agent must guess why it should pick this over epost_download_letter.

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