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/authgear/authgear-server/write-implementation-plannpx skills add authgear/authgear-server --skill write-implementation-plangit clone --depth 1 https://github.com/authgear/authgear-serverWhat 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 | $0.00065 | $0.01156 |
| Opus 5 | $0.00032 | $0.00578 |
| Sonnet 5 | $0.00013 | $0.00231 |
| Haiku 4.5 | $0.00006 | $0.00116 |
Grade A, and why
write-implementation-plan 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 yesterday.
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 — 153 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Write Implementation Plan
Write implementation plans as concrete engineering plans, not design notes.
Workflow
- Read the current spec, the existing plan, and the relevant code paths before writing the plan.
- Consult related skills to understand implementation conventions:
- Check the
add-go-testskill to understand unit testing patterns and whether the package uses Convey BDD-style tests - Check the
write-e2e-testskill to understand e2e testing requirements and patterns - Check domain-specific skills (e.g.,
update-portal-ui,new-siteadmin-api) if the plan touches those areas
- Check the
- Identify the real integration points in code:
- config types and schema
- runtime entry points
- event and delivery paths
- storage and migration behavior
- tests
- Rewrite the plan around the current spec and the current codebase, not around stale assumptions from an older plan.
Requirements
Write the plan with exact implementation intent.
- Name the exact files to create or modify.
- Name the exact methods, structs, and helpers to add or change.
- Describe the exact method call flow for important runtime paths.
- Separate config-layer types from runtime-layer types.
- Preserve existing codebase conventions for file placement and naming.
- Include backward-compatibility requirements explicitly.
- Include deployment and data-compatibility behavior explicitly when storage keys, payloads, or persisted state are involved.
- Include test coverage requirements.
- Include an atomic commit plan.
Do not write the plan at a hand-wavy level.
- Do not say “support this somehow”.
- Do not say “add helpers as needed”.
- Do not say “or equivalent new file”.
- Do not add helper methods that are not used by the plan’s call flow.
- Do not leave known behavior in an “open decisions” section.
Required Detail
For runtime-heavy changes, include all of the following.
Config Plan
- exact config structs
- exact package and file placement
- schema changes
- merge behavior
- migration behavior for deprecated config
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- yesterday First seen · 153 lines · 65 tokens per session scan A 2a86068a86ab
write-implementation-plan is a skill published in the GitHub repository authgear/authgear-server (2,014 stars, last pushed 5d ago), licensed Apache-2.0. It adds 65 tokens to every session and 1,156 once invoked, about $0.0003 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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