Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/plainlang/plain-forge/add-conceptnpx skills add plainlang/plain-forge --skill add-conceptgit clone --depth 1 https://github.com/plainlang/plain-forgeWhat it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00042 | $0.00727 |
| Opus 5 | $0.00021 | $0.00364 |
| Sonnet 5 | $0.00008 | $0.00145 |
| Haiku 4.5 | $0.00004 | $0.00073 |
Grade A, and why
add-concept scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 73 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Add Concept
Always use the skill load-plain-reference to retrieve the ***plain syntax rules — but only if you haven't done so yet.
Workflow
- Identify the target
.plainfile. If ambiguous, ask the user. - Read the file to understand existing definitions, imports, and concepts.
- Validate the concept name against the syntax rules below.
- Check for uniqueness — the concept name must not already exist in the file or its imports.
- Check referenced concepts — any
:ConceptName:used in the definition must already be defined above it (in this file or viaimport/requires). Concept references must not form cycles (e.g., A references B and B references A). - Check for circular references — if the new concept references
:B:, then:B:must not reference the new concept (directly or indirectly). Example of a circular definition to avoid:
Fix by removing the back-reference:- :Order: is placed by :Customer: and contains :OrderItem: entries. - :Customer: is a user who has placed at least one :Order:.- :Customer: is a user of the system. - :Order: is placed by :Customer: and contains :OrderItem: entries. - Insert the concept into the
***definitions***section, after any concepts it references. - Read the file again to confirm correct placement and syntax.
Concept Syntax Rules
- Wrapped in colons:
:ConceptName: - CamelCase, starting with an uppercase letter
- Valid characters: letters, digits,
+,-,.,_ - Must be globally unique across the spec and all its imports
- Exported concepts from
requiresmodules are not transitive — to reference an ancestor's export, list that ancestor inrequires; if a concept is shared across branches, define it in a common import module instead
Definition Format
A concept definition is a bullet in ***definitions*** that starts with the concept name:
***definitions***
- :ConceptName: is a description of what it represents.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 2d ago First seen · 73 lines · 42 tokens per session scan A 8889d7bea979
add-concept is a skill published in the GitHub repository plainlang/plain-forge (55 stars, last pushed 4d ago), licensed MIT. It adds 42 tokens to every session and 727 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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