Read one Codal letter

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

Annotations already declare read-only, idempotent, non-destructive and open-world, and the description layers on real behavioral detail: the tables-vs-text branch, ' | '-separated rows, the unit caveat for amounts, one-sheet-at-a-time paging, attachments often carrying the real content, and truncation at 16,000 characters with a `truncated` flag and a full-PDF fallback.

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 core capability is front-loaded in the first sentence, and every following sentence carries operational information an agent would otherwise have to discover by trial: format branching, sheet paging, attachment caveat, truncation limit. No filler or restatement of the name.

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?

With no output schema, the description carries the full burden of explaining returns, and it does: response variants, row encoding, unit note, paging, attachments, truncation. An agent can call this correctly and interpret the result without further documentation.

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%, so the baseline is 3, but the description adds genuine meaning: it explains that `sheet` ids come from a prior call's `sheets` list and that omitting it returns the first sheet, and it ties `tracing_no` to the value obtained from cd_search_letters.

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?

States a specific verb and resource ('Read one codal.ir letter') and immediately enumerates what comes back: text or tables plus page, PDF, Excel and attachment links. That is enough to distinguish it from cd_search_letters, which only finds letters rather than reading one.

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?

'Use it after cd_search_letters to see what a letter says' gives an explicit trigger and names the prerequisite sibling. It also explains the re-invocation path for multi-sheet statements ('call again with `sheet`'), though it never states when not to use the tool or what a search-only workflow looks like.

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