postbag

by parasxos

Overview Schema Source Related Servers Discussions Admin

Python

Local

postbag_send

Send a letter to a registered peer and record it in the bag; set final to ask the recipient not to reply.

Instructions

Submit one letter to a registered peer and record it in the bag.

final=true asks for no reply. It is guidance, and later letters remain allowed. Requires a current registration in this bag. Never retry an unknown outcome, cancelled call, or timeout before reading the bag and checking the recipient. Does not confirm execution.

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": {
      "to": "<to>",
      "body": "<body>"
    },
    "name": "postbag_send"
  }
}

Input Schema

Name	Required	Description	Default
`to`	Yes
`bag`	No	Default or named bag. Join creates a missing bag.	default
`body`	Yes	Letter text, at most 65536 UTF-8 bytes. No NUL bytes.
`final`	No	Ask the recipient not to reply to this letter.

Output Schema

Name	Required	Description	Default
`ok`	Yes
`data`	Yes
`message`	Yes
`error_code`	Yes
`submission_state`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv2.2.0Oct 2, 2026

TDQS

A4.3/5.0

Behavior5/5

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

Annotations already declare readOnlyHint=false, idempotentHint=false and openWorldHint=true, and the description adds substantial non-redundant context: the operation is non-idempotent and unsafe to retry blindly, delivery is not confirmed ('Does not confirm execution'), and final is advisory rather than an enforced lock. This is exactly the behavioral detail an agent needs and cannot get from the annotations.

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?

Five short, dense sentences with the primary action front-loaded; every sentence carries operational information (final semantics, precondition, retry policy, no confirmation). The telegraphic fragments are slightly abrupt but not wasted.

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?

For a non-idempotent, open-world side-effecting call the critical gaps — retry safety, delivery confirmation, and the final flag's advisory nature — are all addressed, and the output schema covers return values so they need not be described. Nothing an agent needs to call this safely is missing.

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

Parameters4/5

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

Schema coverage is 75%, so the baseline is 3. The description meaningfully extends the schema for 'final' by clarifying it is guidance and that later letters remain allowed, and adds the registration precondition attached to 'to', which the schema does not express.

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

Purpose4/5

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

The first sentence states a specific verb and resource with scope ('submit one letter to a registered peer and record it in the bag'), which is clearly distinct from postbag_read/join/leave. It does not explicitly name or compare against any sibling, so it stops short of full sibling differentiation.

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

Usage Guidelines4/5

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

Gives real conditional guidance: registration in the bag is a prerequisite, and it prescribes the recovery path for failures ('Never retry an unknown outcome... before reading the bag and checking the recipient'), implicitly routing to postbag_read. It never names the alternative tools or states when not to send, so it is a 4 rather than a 5.

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

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