Skill Authoring

SKILL.md Frontmatter

• Required fields: name, description (include trigger phrases so the agent knows when to activate)
• Optional fields include allowed-tools, disable-model-invocation, user-invocable (set to false for background-knowledge skills the runtime loads as context but the user should never invoke directly), and argument-hint
• argument-hint is a Claude Code slash-command UI hint — a string naming the expected arguments, e.g. [init|status|use|uninit|help] [feature]
• This list is not a closed allow-list — agents preserve unrecognized skill frontmatter and ignore fields they don't use (see rules/rule-frontmatter.md)
• The description field is your discovery surface — write it for the agent, not a human audience

Title and Preamble

• Start the body with an # H1 title naming the skill (e.g., # Release Skill for skills/release/SKILL.md)
• The first content line after the H1 declares the execution mode and prevents the agent from parallelizing or freelancing
• Sequential workflows (default — release, deploy, migrate): preamble Process steps in order. Do not skip ahead.
• Action routers (group-management, scheduler-config — agent picks one of several alternatives by user intent): preamble This skill is an action router — pick the step that matches the user's intent and execute only that step. Do not run other steps; do not parallelize. List the available actions in the skill's description so the runtime can match intent

Step Structure

• Use flat numbered headings with descriptive titles: ## Step 1 — Verify Readiness, ## Step 2 — Create PR
• The same flat-numbering format applies to both sequential workflows and action routers — in routers, "Step N" labels each alternative action rather than each phase of a workflow
• No decimals, no sub-steps — flat numbering only
• When inserting a step, renumber all subsequent steps
• Each step is one action. The check is a title heuristic: if the step's title combines two verbs with "and" or "&" (e.g., "Build and Deploy"), split it. A step's body may list sub-tasks all serving one cohesive action
• Action-router preambles are exhaustive on chaining: if a step chains to another ("after registering a group, also configure mounts"), say so explicitly. Default in routers: execute only the chosen step and finish

Step Continuity

• Default handoff between steps is "continue immediately" — never "pause and wait for the user"
• State continuations explicitly ("Proceed immediately to Step N"); do not rely on implicit reading order
• If a step can legitimately end the skill, say so explicitly ("Finish here")

Keep Skills Compact

• SKILL.md is the execution plan, not a reference manual
• Move detailed reference material (API docs, long examples, lookup tables) to separate files
• Reference them with typed code blocks and full relative paths

Typed Calls

• Invoke other skills with typed Skill(skill: "name") calls, never prose references
• Never call Skill() on a rule (rules are auto-loaded, not invoked via Skill)
• Narrow exception for mid-session-install recovery.
• Applies when the authored flow's typed Skill(skill: "name") call targets a skill whose plugin was installed earlier in the same session and the harness throws "Unknown skill"
• Preconditions (all required):
  1. The typed Skill(skill: "name") call stays the sole invocation path in authored flow
  2. The skill text presents the recovery as error handling for the failed typed call, never as an alternative invocation
  3. The recovery reads the target skill's mounted SKILL.md at its plugin mount path (.tessl/plugins/<workspace>/<plugin>/skills/<name>/SKILL.md) and executes its steps
  4. The recovery is scoped to the installing session
  5. The skill text states that later sessions use the typed call
• Every other cross-skill reference is a typed Skill(skill: "name") call

Silence Instructions

• If a step can legitimately produce no output, say so explicitly: "If no issues found, proceed silently"

Script References

• Deterministic operations must be executable script files, not inline code blocks for the agent to copy-paste — see rules/script-delegation.md
• In rule prose, documentation, and skill cross-references, use repo-relative paths (skills/<name>/<file>.<ext>)
• In step bodies, use the path that resolves at the invocation site
• Repo-relative when the skill runs only from a clone of this repo: skills/<name>/<script>
• Plugin-mount path when the skill runs only inside a consumer: .tessl/plugins/<workspace>/<plugin>/skills/<name>/<script>
• A resolved $CP path when the skill runs in both, under the installed-plugin bootstrap in rules/script-delegation.md Scripts Are Real Files
• Don't mix conventions inside one SKILL.md — if one step invokes via a mount path, every other script-invoking step must too
• Include the expected input/output contract in the step description

plugin.json Manifest Reference

The Tessl plugin manifest lives at .tessl-plugin/plugin.json. A plugin distributed through another channel declares the same surfaces in that channel's manifest. The rest of this rule is distribution-independent, save the two provisions that name a Tessl mount path — the Typed Calls recovery carve-out's precondition 3 and Script References' plugin-mount form — which reach a plugin installed at such a path.

Required fields:

• name — <workspace>/<plugin-name> format
• version — semver string
• description — one-sentence overview of the plugin

Optional fields:

• private — true to prevent publishing to the public registry (defaults to true; set false to publish)
• skills — directory path ("skills/") or array of skill directory paths ("skills/<name>")
• rules — directory path ("rules/") or array of rule-file paths ("rules/<name>.md"); every .md file in a declared directory is included
• repository, homepage, license — provenance and discovery metadata
• author — object with name, email, url
• hooks — cross-agent hook declarations keyed by event (PreToolUse, PostToolUse, UserPromptSubmit, SessionStart, Stop), each mapping to hook groups (matcher optional, hooks array of {type:"command", command, args?}); Tessl translates the consensus payload to each agent's native form
• nativeHooks — per-agent hook declarations keyed by agent id (claude-code), same group shape, written straight to that agent's native config

alwaysApply and applyTo: are not manifest fields — rule scope lives in the rule file frontmatter per rules/rule-frontmatter.md.