Letter IRL

Sign or unsign a letter

set_letter_signature

Idempotent

Print the person's saved signature on a previewed letter, under the closing, or take it off, without previewing it again. Give the draftId from the preview and signature: true or false. set_signature saves a signature first; true with none saved is refused. The signature takes 3 lines, so a letter with no room for them is refused. The page is drawn again with the signature as it is saved now, and the choice is remembered for the next letter preview.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "draftId": "<draftId>",
      "signature": "<signature>"
    },
    "name": "set_letter_signature"
  }
}

Input Schema

Name	Required	Description	Default
`draftId`	Yes	The draftId from a letter preview
`signature`	Yes	true prints the person's saved signature under the closing; false takes it off

Output Schema

Name	Required	Description
`pages`	No	Present only for a letter of more than one page: the pages it prints on, both sides of the paper. No letter pack or gift letter pays for it; it is paid with Pay & Send.
`draftId`	Yes
`message`	Yes
`signature`	Yes	Whether the letter now prints the person's saved signature: asked for in the call
`canSendNow`	Yes	Whether the balance or a gift letter pays for the letter as it is now: the signature's lines can change its pages, and so its price
`mailService`	No	With the terms, for a letter that is certified mail now, and for a sent letter that went by it: which service. Absent beside the delivery words: ordinary mail
`deliveryClass`	No	With the terms, for a letter that is certified mail or while certified mail is offered, and for a sent letter: how it is delivered, as a new preview would say it. A card draws it on its Delivery line
`contentVersion`	No	The version of this mail as it is now: send it with the send, so what is mailed is what the person saw
`sendEligibility`	Yes
`reasonCannotSend`	No
`deliveryDisclaimer`	No	With it, the words that qualify the delivery
`contentVersionBefore`	No	The version of this mail the change was made to: for the preview card, which takes contentVersion only when this is the version it shows

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 7, 2026

TDQS

A4.6/5.0

Behavior5/5

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

Annotations only declare it non-read-only, idempotent, non-destructive, and closed-world. The description adds substantive behavior beyond that: the page is redrawn with the currently saved signature, the choice persists to the next preview, and the operation is refused when no signature exists or when the three-line block does not fit.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loads the action and stays compact, with each sentence adding a distinct fact (precondition, alternative, refusals, persistence). The middle sentence restating the two parameters duplicates the schema and could be cut.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return values need not be described; what remains — preconditions, refusal conditions, redraw behavior, and remembered state — is all covered. Nothing an agent needs to invoke this correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so both parameters are already documented in the schema, and the description largely restates them ('Give the draftId from the preview and signature: true or false'). The one piece of added meaning is the clarification that the signature printed is the one 'as it is saved now', which the schema does not say.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource — print or remove the saved signature on a previewed letter under the closing — and explicitly contrasts with set_signature (which saves a signature) and implicitly with clear_signature. An agent can distinguish this from the sibling tools without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives the precondition (a draftId from a preview), the alternative workflow (set_signature saves the signature first), and the exclusion (true with none saved is refused). It also notes the no-room refusal, so the agent knows both failure paths before calling.

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

All Letter IRL tools Inspect

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