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The agent loop

When an agent receives a task, it follows this flow: 
User message
    ↓
Agent scans available skills (reads SKILL.md descriptions)
    ↓
Agent selects matching skill(s)
    ↓
Agent reads full SKILL.md for usage instructions
    ↓
Agent runs commands / scripts as described
    ↓
Agent reads output and responds to user
There is no capability negotiation, no handshake, no initialization sequence. The agent reads a file and acts on it.

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Discovery

Skills are discovered through the filesystem. An agent knows about skills in its configured skill directories. When a task arrives, the agent scans skill descriptions to find relevant ones. 
~/.skills/
  github/SKILL.md
  weather/SKILL.md
  database/SKILL.md
This is analogous to how a developer scans tool documentation — read the description, decide if it’s relevant, read the details if so.

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Execution

When a skill includes executable scripts, the agent runs them as child processes: 
# Agent decides to use the weather skill
./weather/run.sh "Tokyo"
# stdout: Tokyo: ☀️ +15°C
The agent captures stdout and uses it as context for its response.

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Environment variables

Skills can receive configuration through environment variables. This keeps secrets out of command-line arguments (which appear in process listings). 
# Agent sets env before calling
GITHUB_TOKEN=ghp_xxx ./github/run.sh pr list

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Exit codes

  • 0 — success, stdout contains the result
  • Non-zero — failure, stderr contains the error message

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Composition

Skills can reference other skills. A “deploy” skill might call a “git” skill and a “docker” skill internally. This is just scripts calling scripts — no orchestration framework needed.

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What SCP does NOT define

SCP intentionally avoids specifying:
  • Transport protocols — there is no transport; skills are local files
  • Authentication handshakes — use environment variables or config files
  • Capability negotiation — the agent reads markdown; it understands what it reads
  • Lifecycle management — no connections to open or close
  • Streaming protocols — stdout is already a stream