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Postal mail API and MCP server for AI agents: send letters, certified mail and postcards, and give an agent its own street address + PMB with webhooks, OCR search and human-approved scan, forward or discard.
Postal mail API and MCP server for AI agents: send letters, certified mail and postcards, and give an agent its own street address + PMB with webhooks, OCR…
As a process C 50/100 · Has gaps — weak spots: result and completion, when it triggers, inputs and preconditions
What is at stake
Medium-severity findings: the skill is probably honest, but read what alarmed the scanner.
Below is the worst case for this category. The finding here is medium: the guard saw a sign, not a proof.
The instructions or scripts send data out: environment variables, keys, file contents, chat history. You may never notice, because the agent performs the upload as "part of the task".
If the upload is not needed for the task, remove it: catalogs flag such skills and delist them. If it is needed, name the destination explicitly, say what leaves the machine, and give the user a switch.
How to improve
- Your own cases (evals/evals.json, 4–6 real requests with expected answers): the full check would then run those instead of a model-drafted suite.
- A spec.yaml with trigger phrases and assertions — a behaviour contract for CI; `skilltest init` writes a template.
Guard findings · 3
✓ No critical or high findings
Medium and low: 3
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medium Exfiltration
net-credential-useSKILL.md:138Credential used in a network call (verify the destination is the intended service)curl -s "$MAILBOX_BOT_URL/v1/inbound-items?q=irs&limit=20" -H "Authorization: Bearer $MAILBOX_BOT_API_KEY"
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medium Exfiltration
net-credential-useSKILL.md:139Credential used in a network call (verify the destination is the intended service)curl -s "$MAILBOX_BOT_URL/v1/inbound-items/{id}" -H "Authorization: Bearer $MAILBOX_BOT_API_KEY" # version, actions, quotes -
medium Exfiltration
net-credential-useSKILL.md:140Credential used in a network call (verify the destination is the intended service)curl -s "$MAILBOX_BOT_URL/v1/inbound-items/{id}/pages" -H "Authorization: Bearer $MAILBOX_BOT_API_KEY" # OCR per page
Files scanned: 7. Evidence is masked. Grey chips explain why severity was lowered.
Against the Agent Skills spec
- note
frontmatter-keyunknown frontmatter key "repository"
Process rating: all ten parameters 50/100
- 0Result and completion. Does not say what the result is
- 0Inputs and preconditions. Does not say what the process needs to start
- 20When it triggers. No condition that starts the skill
- 30Running it twice. 23 mutating operations with no state check
- 50Failures and branches. 0 branches, has a failure section
- 60Tools and files. Uses tools (web) that frontmatter does not declare
- 100Steps. 25 steps
- 100Consistency. Name and required fields are in place
- 100Execution cost. Instruction body is 2803 tokens
- 100Progress reporting. Reports progress
- medium Safety rules and hard prohibitions inside a skill: they belong in the system prompt, here they protect nothing
Everything here is measured from the skill text rather than judged by a model, so the numbers are checkable. A parameter weighs more when it is a more common reason for the process to stall.
Quality signals
- +5Description has no quoted example phrases that should trigger the skill
- +4Description does not say when NOT to use the skill (false activations)
- +3Output format is not stated: the model decides each time
- +1No license
- +2Single-language instructions
- +3Description length 207: enough signal without eating the budget
- +4Structure: 10 headings
- +3Step-by-step instructions: 25 items
- +4Has examples (7 code blocks)
Quality base 70; lint remarks subtract, signals add up to 100. Result: 83.